Yes, you are definitely allergic! I have been stung by a wasp twice on the hand, and both times my hand swelled up like a sausage, but nothing else happened on the rest of my body. Definitely mention it to your doc -- she may recommend an Epi-pen to carry with you from now on. Often the second or subsequent stings are much worse for those allergic.

Hope you're all better soon. Benadryl is definitely a good idea in the meantime.