Your post is quite confusing, at least to me. Was it the vitamins or the zinc that said it contains wheat? If it's the zinc, why does your title say there's wheat in the vitamins. If it's the vitamins, what does the zinc have to do with it?
Seafood caused me no problems whatsoever, and I had DH for more than 20 years. Oysters are lower in iodine than many other things, including milk, and prawns are actually very low (shrimp is much higher).
Might be something psychological going on. You expected itching and you got it.
Glad you feel good AND that you took this step, but I hope you also learned that you HAVE to question everything. And the server absolutely must check with the kitchen. I don't like doing it, either, but it's necessary.
I know that doctors aren't always helpful, but if you haven't seen yours with these returning symptoms, you should. These are some serious symptoms that might not even be related to what you're eating.