Suggest Medication For Skin Rash

I have skin rash from last night. I first thought it's a food allergy, and took Benedryl. It was horrible all over my body was covered by rash (more likely hives), but it stopped after the med. I was fine this morning and went to school, and start having the rash again. I'm not sure if it's food allergy, which I've never had before, or some paint chemicals at the school since they just finished the fresh paint. If it's food allergy, I think it should have been gone by now, but I still have rash around my neck, legs, feet and arms...
I went to a drug store during my break at school, and took Claritin, but it still itchies...