I had allergic reaction for an antibiotic. Is it normal for it to keep spreading?

Hi doctor,

I recently had the flu that is going around. During it, my GP prescribed me Erythromycin because she thought that I had a bacterial infection in my throat. Whether or not she was right, I suffered an extreme allergic reaction to the antibiotic, which I had used before without side effects. Another GP yesterday told me to stop taking those pills. She has prescribed me a strong antihistamine, Fexofenadine hydrochloride 120 mg, one to be taken once a day for a week or until the hives have cleared up. The rash started on my neck and spread across my body. It takes the form of tiny red dots like pimples, but not pimples. It does not itch. I took one Cetirizine three days ago and now I have taken two of the other antihistamines as of this morning. I am applying Hydrocortisone topically. It is now four days since I stopped taking the antibiotic and overall I had 17 pills. It is now two days into the stronger antihistamine. This morning, I notice the rash has spread down to my lower legs and feet. It is noticeably better in my neck and upper part of the chest. Is this normal for it to keep spreading as a result of an overproduction of histamine by the body in shock? How long will it take to clear? Will it be clear completely? Are there better private medications or topical treatments to take if I want 100 % clearance of it? Please advise.