I Used To Enjoy My Food

I used to enjoy my food and there was nothing better than a home cooked meal .Since leaving hospital 4 years ago , eating has become a neccessity and I get no enjoyment at all from it because after I eat it makes me feel sick to my stomach , at times so much so that I am bent double and feel like I want to throw up but never do .The strange thing is I have oatmeal porridge for breakfast with no unpleasant side effects but if I eat meat and veg etc in the evening I feel sick as a pig .
I have sought medical advice but no one seems to know whats causing it .I have had alsorts of tests and no answers its really frustrating .