Food doesnt agree with me anymore please help? Thanks?

Ok so heres the thing i always make my self sick when i eat i have for 4years..but no i dont even have to do that cuz when i do eat i get such a sore stomach and it goes straight threw me..and i start swetting up and my stomachs sore for ages..why is this? Now i'm too scared to eat cause dont want that happenin one more time :(