First of all: welcome! Glad you found us!
I would not
try crawfish on your own without having done a food challenge by a board certified allergist. Yes--there are different proteins involved. You can be allergic to one fish and not allergic to others, or as you've found out, even though they are quite similar, not react to certain shellfish.
This might be helpful: Nice Summary of Shrimp Protein
But it doesn't address the different proteins in various shellfish.
I'm allergic to shrimp and lobster but I do believe my crab allergy may have gone away. But I will get a challenge before I eat it (all were adult onset around 40 years of age after moving to the Houston area and consuming a lot more seafood than usual). And here's the thing, it's not like it's easy to find varieties that are not cross contaminated. I won't even buy fish in the grocery store because of how it's typically handled and displayed--cross contaminated with shellfish. Although my current grocery store (we have recently moved to a larger metropolitan area) actually has separate cases for shellfish and fish.
And there is the possibility of buying fish at Kosher markets in my new city. (My son is vegetarian, so we don't really eat much meat at home, so I have not been motivated to seek out safe fish).
So if you ate lobster safely, I think you were very lucky. In a restaurant setting and in grocery stores, lobster is quite likely to be cross contaminated with shrimp.
About being newly diagnosed with a plethora of allergies--if some of the new ones were through skin prick test only, I'd be wary of accepting those results. Skin Prick Tests have high false positive results. If the doctor did an SPT for foods you were already having problems with or if they were confirmed with blood test results, I'd be more likely to accept them. That said, I don't recommend just going out and eating things your doctor said were positive on the tests. I would get advice from him or her.
My son's blood tests--taken in January and last week--were different for kiwi. In January a blood test said he was allergic to kiwi and shrimp (news to us) and peanuts (not news). Last week shrimp and peanuts were still positive, but kiwi was gone. We had doubted kiwi was a problem but had been avoiding it for the last few months.
Also--note that a reaction does not have to involve breathing difficulty to be dangerous/anaphylactic.
I'm glad you found us! I hope this is a helpful place for you.