Recurring fever in 2. 5 years old.

My son got a fever around 1st week of October that lasted for 4-5days. His CBC showed elevated neutrophils though wbc was within limits. He also had high crp. There was no cough or cold. Blood culture was Normal; but the fever went only with an antibiotic. The second episode of fever happened on Nov 2 and lasted till nov 7; both episodes fever touching 104 in the armpit. He then had a mild fever a week later; went with a call dose n never came back. This happened twice in a gap of about a week. Since yesterday he again has fever. He was perfectly okay till about 5.30pm. we went out; by the time we came back around 7pm he had 102.5 in the armpit. We have been alternating meftal and calpol. What could be the reason for recurrent fever. Is calpol/meftal safe in such a scenario. I am really worried and want to know if it could be anything more serious.