Why am I allergic to restaurant lobsters only?

I used to eat lobster and crab when I was young. I stopped about 20 years ago when I had several allergic reactions to restaurant lobster and crab. However, I can still eat lobster bought live and cooked at home. I was wondering if restaurants add something to the lobster that would cause the reaction. I have no problems with shrimp, scallops, mussels or any type of fish.