As people have said, you can develop allergies to pretty much anything at any point in your life. Most allergies develop over time and exposure, and aren't with you from birth.
Just because you're noticing them now doesn't mean that being veg is what caused them. Though if you're like most vegetarians, you're eating a LOT more variety than you did as a meat eater.. that's how I found out that I might be allergic to eggplant. Never ate it before going veg. It makes me feel sick half the time so I avoid it.
Regardless, I seriously hope that you do research, allergy tests, and so on before making a leap to quit something that you say you care about. If you feel tricked into it, maybe you need to re-evaluate WHY you went veg in the first place. If it was indeed for health, look at health sites. Look for medical sites. I know there are very many heart health sites that promote veggie diets for patients, for heart health. Just make sure you're getting medical information from unbiased sources - PETA is good for the "this happens to animals" slant, for sure, and if that's a reason you went veg, and want to stay veg, keep looking there for that kind of thing. But unbiased medical research on humans regarding veg diets, not paid for by meat/dairy or veg groups, is what you should look for.
Do what you think is right, but no one can force you into a decision to go veg, it's 100% your choice to make, so if you felt that someone misled you... well, look in the mirror, and figure out why you really made the choice in the first place.
Best wishes whatever you decide to do.