I had an allergic reaction to poison ivy several weeks ago. I went to a clinic and was prescribed prednisone, in fairly heavy dosage. That is now done. I ve had this problem several times in the past and the steroid knocks it down. However this time my right arm has become red and swollen around the areas where the ivy blisters popped up. The blisters are drying up but redness has spread outward. I urinate often, my throat is a bit raspy. Reading up I believe I have cellulitis and have had this for about 4-5 days. It s not getting worse but not much better either. I have some penicillin and just took a pill ( VK 500 mg). But, I don t have enough for a 10 day regimen.