I'm sorry you are having such a difficult time! The good news is that seeing a doctor has ruled out different things. And you do indeed sound stressed and anxious. When I was in college and wasn't sleeping well, studying, working all the time, I had fitful sleep. I even would sleep walk. This does not happen now. Could you try something like melatonin (which you can get from any health food store) which may aid your sleep without making you groggy? And do you have good habits like no caffeine after say 6 pm. limited eating and drinking from 7 or 8 pm on, dark, cool room? White noise like a fan really helps. I do have times when I'm roasting when I get up (typical for me) and then get cold and chilled and go back to sleep feeling cold and can't warm myself. Not sure why. I just roll with it and assume it is hormonal in my case.
I know I'm of no help but I would try to reduce your stress. It's hard in school, but do your best. Try to exercise during the day as well as that aids sleep and is a natural stress reducer.