Keflex and stomach

I have been taking keflex for 3 days for severe cellulites on my right leg that was caused by an insect bite. I am allergic to penicillin, which the doctor knows. The pharmacist did counsel me and I knew. I have developed itchy patches in a lot of places, especially my face. So far it is not bad enough that I can't handle it. I am not ready to throw in the towel yet and try something else though because I know it is supposed to be effective against what ails me. I was bit by a brown recluse spider in 1984 and as a result I am concerned about how bad a skin infection like I have can get (even though I am sure this time the insect that bit me was not a poison spider). I have a few mild other symptoms (stomach, back, tired) and I have been feeling a little blue also but I am not sure whether keflex is the cause of any of that, or if it is the bite.