Why do I get an upset stomach after eating out?

Whenever I eat out at a restraunt, I always get an upset stomach and bloating. It mainly happens with meat products. Steak, a good burger, ribs etc. After 20 or so minutes when I am done with my food, I always get an upset stomach. It swells and well.. turns into "hershey squirts." Now I cook alot of my own BBQ and steaks and never have this problem with the food I cook. Why does this happen?