My 2 year old has been experiencing a persistent low fever (never dropping below 100 and often rising to 100.5-101 and higher) for about a week and a half. He first started with symptoms of a cold, sore throat, croupy cough, runny nose. After his fever did not go away the dr. said he probably had sinusitis and treated him with an antibiotic. He has been on that for 4 days and the fever is not gone however his cold symptoms are. Should we still be concerned about the fever?