iThink virus—specifically coxsackie virus, otherwise called hand, foot, and mouth disease. Viruses don’t respond to antibiotics. The main thing to do is to make sure the child drinks fluids to prevent dehydration. Any fluids without caffeine will do. it can also be Scarlet fever. This is merely a strep infection with a rash. The child usually has a sore throat, but not always. That’s because the strep infection can be on the skin, even in the urine. Treat with an antibiotic such as amoxicillin, penicillin, or erythromcin. The child will usually get to feeling better in about 72 hours. It’s important to take the antibiotic for ten days to prevent the risk of rheumatic fever. if you have already used any of the antibiotics above mentioned and rash appeares after fever it can be due to antibiotics also you can try benadryl syrup.if you can not understand consult the doctor .