Why does my stomach hurt every time I eat crab?

I got tested for my allergies and seafood isn’t one of my results so I’m not allergic. But usually, when I eat crab or have a seafood boil I’m doubled over in pain later on. I can eat shrimp just fine, it’s only crab that gives me issues. Does anyone else have that problem? If so, do you have any remedies to fix or prevent it?