What Causes Extreme Fatigue Despite Sleeping Well?

I am exhausted even after sleeping 10-12 hours. I do not snore or have sleep apnea. I crave sweets, even steak, which I usually love doesn t taste good. I am on antidepressants, but still seem to have no motivation to exercise, lose weight (5 3 212 lbs.), do the things I used to enjoy. Have terrible memory problems, reading retention is no where near what it used to be. Trying to continue my education and have to continually reread things because I can t remember what I just read. I am 55, and through my change , but am starting to have hot flashes again. Sometimes my back feels like it is on fire. Help me please.