My Stomach Always Bothers Me After I Eat Dairy Or

My stomach always bothers me after I eat dairy or oily things. I've tried lactose pills and it didn't work. Also, basically anything unhealthly bothers my stomach. Some examples and donuts, ice cream, or cake. I am vegetarian but even before that I had food problems. I even take b12 and everything. I can't dip my bread in strait oil like olive oil either. It really sucks and I've asked doctors and they just say I have a sensitive stomach.