I was prescribed sulfa for 10 days, twice a day for an upper resp...

I was prescribed sulfa for 10 days, twice a day for an upper respiratory infection. Today is the 8th day and I woke up with hives all over my body, mostly my chest and thighs. I had taken my pill this morning as per the usual because my doctor was not open yet. He instructed me to stop taking it because I'm allergic. Apparently it takes a week to manifest itself (the allergy). So I'm done with the pills and hopefully the infection will clear up on its own. But im so itchy!!Benadryl was recommended for that.