How Can Fever In An Infant Be Treated?

My son Yuvan, 9months old, 9.5 kg, having fever since last 2 days. At very first day of fever, we gave him T-98 but fever was still there then next day we gave him P-120, fever was still there. we measured his fever hourly and almost every time it was above 100F. yesterday night we gave him combiflame syrup 5ml, we found the fever was settled down for 7-8 hours. This morning fever is again high and he also vomits 2 times. After giving 2nd does of combiflame syrup this morning his fever again settled down but now again after 7 hours he has fever above 100F. Can we give him does of combiflame now? Why fever is going and coming? Why fever was not set down with T-98 or P-120? worried...