When I was 3 or 4 months pregnant, I develped HIVES all over my body for like a month or more and was on I think, Benedryl. I was also testing positive for rheumetoid arthritis, but after I had my son months later, I tested negative. It is weird how pregnancy brings stuff out in people. Sometimes I believe it is a trigger for things we have in us that we may have never knew about. It does sound like an allergy. Just think of what you ate the night before that may have triggered it, but definatly talk with your doctor, it won't hurt.