Seafood...

I was eating crab at Guangjie and Liuqin's house.But my lips start to get swollen just minutes before we finish it.I always took that I am alergic to seafood which are not fresh.But the crab must be fresh because it was only killed and cooked.
Have to find out why am I alergic to seafood.Or am I just alergic to all seafood?I don't really think so!