Every morning I wake up with a sore throat.
It usually burns off around a hour later.
Why and how can I prevent it.
Some general facts: I sleep next to a tiny wall heater that I have going full blast all night in order to keep he room from freezing.
I sleep on my stomach.
I usually get between 7 and 8 hours of sleep a night.
WAG, this is probably the cause. Heat will cause you to dry out and make your throat parched and hurt to swallow. I would also ask if you smoke. Try sleeping without the heated and/or keep a glass of water by your bed and take a drink if you wake up in the middle of the night.
You are dehydrating over night. Get yourself a humidfier and run it in conjuction with your heater if you want to keep it running all night, sweets, or all your tissue will look like an old wallet come morning.
Having a glass of water by your bed is a good idea but drink a lot when you wake up too, juice or water is best.
Well Mr.Green, I’d definitly say the heater is drying out your mouth and throat, and that is the very reason you have a raspy nasty funk going on in your mouth in the morning. Couple options, (1) buy a humidifier->problem solved (2) don’t sleep next to the heat source.
By the way this can also happen whilst sleeping next to a wondow as well. The humidifier is the best bet.
Do you know if you breathe through your mouth when you are asleep? (or snore for that matter?) I do (both) and wake up with a parched mouth - although not the raging sore throat that you describe.
Try drinking a glass of water last thing at night…
Gp
Dry air or could be nasal drip as well.
Or it could be all the talking in your sleep… 
Just kidding, it’s the heater.
I often wake up with sore throat and dry mouth and it is because I have been sleeping with my mouth open (and probably snoring). If you can find a way (probably position) to keep your mouth shut while you sleep, I think the problem should disappear.
If it isn’t because of dry air from the heater, it could well be postnasal drip as suggested by Philster.
A lot of people have allergies that cause the tissues inside their nose to swell and secrete mucous. During the day while they are walking around they may be able to breathe fairly normally and don’t notice the postnasal drip because they are swallowing fairly frequently. But at night, it is too hard to breath through their noses so they breathe through their open mouths and the post nasal drip runs into the back of their throats where it causes and irritation that they notice when they first get up in the morning.
Can you breathe freely through both nostrils during the night?
Another cheaper suggestion before buying a humidifier is wetting a towel completely with water and hanging it somewhere close to where you sleep. And you can also buy a face steamer for about $20 and use it in the morning and before bed. Not only will you have a nice complexion but also your throat will feel better:) .
blows hot air just above the floor (and is out of the traffic pattern):
get one of those foil roasting trays, place about 1" of water in it, and place it on the floor in front of the heater: instant humidifier.
(adjust water lever to allow for critters mistaking it for water bowl)
my guess is you have sleep apnea. this is a condition where you wake up over 100 times a night without knowing. it causes major throat soreness.
check it out on the net and see if you have other symptoms of sleep apnea. it is a horrendous problem and can lead to an early death. the main symptom is you are tired all day from lack of sleep.