I'm perpetually cold. All the time.
My primary doctor claims it's caused by my deteriorating thyroid, but I don't have any of the other symptoms. So I blew off my doctor, told her to stick her stethoscope where the sun don't shine and put on an extra pair of socks. I know it started a couple of years ago when I lost a lot of weight. I've read that a lot of people -women in particular- suffer from cold after weight loss because... well, to be honest, we're losing blubberesque insulation. We transform from crooning whales to chirping dolphins. Since then I've become more active. Probably more active than when I was younger.
I run, walk or do some form of cardio every day. It's not so much a workout routine as something to keep boredom away. Despite all my activity and my awesome metabolism and my drive to go outside and DO something rather than watch television all day, I'm insanely cold. Nights in the fall are pretty bad, but only because winters are worse.
I tend to sleep with socks on, flannel pants and as many comforters as I can pile on. Even then, I vividly remember nights where I lay shivering for an hour under a mountain of blankets and countless layers of socks and long-sleeved shirts under short-sleeved shirts under sweatshirts. I just can't get warm and at that point I get scared. How would I survive if I were to be displaced somewhere further north?! I would most certainly die from hypothermia and be as blue as a Smurf until a group of adventurous aliens abduct my corpse and attempt to explain to their elders just why the human race suddenly diversified to include primary colored skin pigmentation.
I've come across a few things that help remedy this problem. They certainly will not help everyone, because they do not always work for me; some nights are worse than others.

1) Jumping rope/Jumping jacks right before bed
    The point is to raise your body temperature to a point that is normal and healthy for you. You don't want to get sweaty, but be vigorous enough to spike your metabolism. Take deep breaths to bring oxygen to all your muscles and you will feel your arms, legs and chest begin to warm- Why? Because turning oxygen into energy makes friction which causes heat. Everyone knows heat rises, so the heat from the expired oxygen moves from the muscles up to your skin. Yay, science!
   When I do this, I start out wearing as little as possible (e.g., t-shirt and shorts) and run through a minute of jumping rope/jacks. Then I throw on my heavier layers and dive into bed, always making sure to tuck the ends of the blankets under me so the cold air from the outside sneaks in when I shift position.
2) Bed Buddy
    This part can be as PG13 or NC17 as you want. I usually call in my dogs and, being Golden Retrievers,  they snuggle in as close as they can on either side- another reason why it's good to have more than one dog: you're the hotdog and they're the bun! However, since they are dogs and not people, they might switch rooms in the middle of the night. For me, this isn't a problem. I have trouble falling asleep in the cold, not staying asleep in the cold. I'm sure that if you have dogs and want them to stay by your side throughout the night you can train them, shut your door or strap them to the bed against their will. After all, if you freeze and die in the middle of the night because they decide to wander off, who will give them bacon for breakfast? Of course a healthy alternative would be your partner but if you're easily distracted and one of you is feeling frisky, sleep will be the last thing on your agenda.
3) Easy Layers
    If you have trouble getting warm, but stay warm once you hit a certain level of temperature, it's best to wear layers that are easy to take off in your sleep. Otherwise, you'll wake up to a puddle of sweat. Socks are easy to push off if you're either half-awake or completely asleep (I once found four pairs of socks I thought had been thrown away tucked into the foot of my bed and have no recollection of putting them there myself). T-shirts are easy to pop off or lift up to get ventilation. Don't forget about layering comforters and blankets so if you push the top layer off, you'll still be able to stay warm without suffocating. And never forget about popping your arms out from under the covers to get some air.
4) Hats
    Hopefully your mother has told you before I have, but you should really wear hats when you go outside to play in cold weather. Fall sporting events usually feature entire stadiums of vibrant-themed hats, skiers wear hats and so should you. The more skin that is exposed is more surface area prone to heat conduction- when two surfaces touch and transfer heat. Heat automatically moves toward colder areas (just look at weather patterns) and cold slips right in once heat is gone. So if you're outside and it's fall and the leaves are falling and the air is crisp with that smell that reminds you of snow... you are capable of losing up to 40% of your body heat through the exposed surface area of you head. The face, scalp, neck and ears are all vulnerable. So if you wear a hat outside and stay warm, what's to stop you from wearing a hat to bed?
    OK, so it might not be terribly sexy, but it could be fun! Also, pick a style of hat that isn't stifling. No faux fur hats that might irritate your skin, no stylish hats with loose string or fabric that might get caught around your neck, in your mouth, on any jagged or sharp edges near your bed or caught in any piercings-ouch! A knit cap might be plain, but it will probably do the trick.
5) Liquor (21+, please)
    Not a fan of snuggling/hat hair/fussy layers/aerobics? Liquor has been known to bump up your internal temperature since before the colonial days. My own Gran has admitted to spiking her children's hot toddies with rum after a day in the snow! Not only that, but as a depressant, liquor will also increase the "sleepy" feeling because it slows down the nervous system and help suppress any early-night cold spasms you might have.
    Listen to me, though: a shot per night will do! I'm not saying it's OK to down a fifth of Wild turkey just so you can feel your toes.
    Pour a thimble of whiskey into your evening coffee or tea-preferably decaffeinated- or whip up a spiked milkshake. Pies, cakes, bread puddings or snacking cookies infused with bourbon, scotch, rum or brandy will do, too. They may be fattening, but the warm factor will carry on through the your pre-bedtime activities such as brushing your teeth and right when your head hits the pillow, the liquor will hit you.

This isn't scientifically proven in any way, nor is it endorsed by any health-guru such as Dr. Oz or whatever quack they have on TV now. But these remedies are cheap, easy-to do, and they usually work.
I still get cold spells, but I'm working on it: During the day I drink hot-hot-hot green tea, hot chocolate or cider. The afternoons are spent doing cardio or aerobic or light-weightlifting and when I spend evenings outside I always make sure I have multiple layers ready. I keep a blanket in my car for star-gazing, sweatshirts and hoodies by my bedside and I always keep my warmer socks on hand throughout the year, regardless of the summer weather. Do what you can do, that's all I can say right now.