Allergic to penicillin?

I'm on penicillin and I noticed a weird rash on my chest. I figured I'd call my mom and ask her if it could be caused by the penicillin and she told me that I'm allergic to it? She told me it always made me break out in a rash since I was a baby and she would stop giving it to me and give me Benadryl and the rash went away. She told me she doesn't know what else would happen if I keep taking it. I took the last one today and I don't have any Benadryl and the rash is spreading to my arms, back and torso. I'm really itchy everywhere and I'm not sure what to do.