What Causes Rashes On Arms And Legs Inspite Of Taking Benadryl?

I have a rash a on my arms, hands, abdominal, left foot and chest that itches like crazy. I have been taking Benadryl for three days now. Initially the rash was only on my left leg and left foot but has spread rapidly. I had foot surgery on March 2 and the incision is infected. I just started my second round of antibiotics this afternoon. I am allergic to several medications and latex along with bee stings. This is not like a typical medication allergic reaction for me. What do you think it is?