Doctors don't know what's wrong with me?

I'm tired all the time, I can fall asleep for a few hours round about the early evening time. I do sleep well but I'm still tired when I wake up. I could happily stay in bed all day, but no amount of sleep refreshes me. One of the few things that wakes me up is eating or drinking alcohol (when I'm around other people in a night out situation I feel great) and no I drink about twice a month if that, I'm not an alcoholic. They've given me numerous blood tests and ruled out being anemic, having an iron deficiency, and diabetes. I have ulcerative colitis, could it be related to that?