I Had A Wasp Sting 1.5 Days Ago. As Had

I had a wasp sting 1.5 days ago. As had antibiotics before fir it, I went to Emegency. Doc urged me to get OTC allergy medicine and wrote a prescription for 500mg cephalexin. I had two allergy tablets (Claritan) and overnight, redness increased and infection moved from sting upper arm close to armpit to elbow. I filled the prescription and at 2 pm today, took a pill and have had three now. The info sheet says it takes a few days to act. I see no lessening and am worried. The infection has increased in size, itches and hurts. I just took a third Claritin and am using ice pack to help stop swelling. Should I return to ER?