Heavy cough with Viral fever. For this.

Dear Doctors - My baby is 6 months old weighing 10 kg having severe caugh and fever 102 degree while checking Pediatrician they gave medicines and asked to take nebuliser for 3 days morning and evening. Prescribed dose levolin 5 ml(0.63mg), duolin 3ml, budecort 4 ml(0.5mg). First two days fine fever settled only medium caugh was there but third day after Giving nebuliser he had continuous caugh and fever the same night and he did not sleep. Felt very tired again fever increased to 101 degree. Again visited Pediatrician fever settled blood report normal X-ray said he is having viral fever. Now the doctor recommended to give nebulizer once in two hours but after giving I can see sudden spike in temperature to 101 degree. So my question is what could be the reason for this.