My 3 Year Old Has A Bite Mark On His

My 3 year old has a bite mark on his ankle that I noticed yesterday. It looked swollen and red around it and itchy. Now there is more swelling and redness above the bite mark. I think it may be from him scratching it so much, but I am not sure. He complained of groin pain this morning and has a bit of fever. He is crying a lot and seems to be in pain. I put some Benadryl anti-itch cream on it and he was hysterical. He has a history of crying a lot over just a hang nail. Should I take him to the ER or wait it out to see if his conditions improve?