Allergic to seafood?

I just turned 30 and have been eating seafood for as long as I can remember. A Few months ago I ate salmon cakes a got itchy but thought nothing of it. I've had fish, shrimp, tuna, and crab Spreaded throughout the months and all those times I've became extremely itchy. No hives or throat closing up. Is It possible to be allergic to seafood now after all these years? I also have a brother who has been allergic to seafood his whole life. He told me welcome to the club lol. I hate this, I love seafood!