sick and scared.

I'm scared... I'm 19 years old and for no apparent reason my health is deteriorating. I haven't been on here much lately because of it. It has happened so quickly. I've lost a lot of weight just in the past 2 months and we can't figure out why. I've never been really big to begin with, so weight loss is not a good thing. I am away at college so I don't see my family too often. I went home for thanksgiving and my mother got very upset with me about my weight. I understand that she is worried, but I've tried everything. I cannot help it. I'm down to 91 lbs. I'm starting to look scary and sickly. I do not have and eating disorder, but a lot of people are accusing me of it. It is frustrating. Things are becoming dangerous and we cannot figure out why or how to make me gain weight again. I hide my emotions, but inside I'm terrified. I don't know what to do. Please help.