Dear friend regret for writting late ! If your baby has just fever and is otherwise active and accepting feeds with no vomits ,its more likely of a viral origin.Keep paracetamol available and as and when required (when body temp is more than99F),give 6 ml from 120 mg per 5 ml suspension .Hope your baby weighs around 10 kg . it might take 2-3 days to settle .If any other symptom as mentioned earlier appears then pl.see your doc..Take care