What Causes Sudden Weight Loss And Body Pain?

I've been to the hospital been to.my family doctor and still no answers as to why I've lost 90 pounds why im having pains in my stomach and why my whole body aches on a daily basis. Alls they keep doing is giving me pills. Their not helping. Their making it worse on me. I feel like I'm shutting down I'm 18 and I'm 109 pounds at 5'7 1/2