What is wrong with me?

I am 26 yrs old 5"6 123 pounds. People tell me all the time im pretty. I know im not fat but when I look in the mirror I see a fat gross person. It has worsened since my recent engagment. I weigh myself 6x a day and get very depressed if I gain even a pound. I take laxatives exersize obbsesively and cant take more then 2 bites of food without felling sick. Ive recently started taking diet pills. My fiance has no idea whats going on. I cant stop this obbession and dont know what to do. I have lost alot of weight in the last 2 weeks and my fiance tells me how good im looking and it makes me think maybe I dont have a problem and im right I was fat before.