Suggest Medication For Fever, Congested Sinus And Abdominal Pain

My son has had a fever of 101 since Saturday. We went to the urgent care (just moved to new area no dr s established yet) and they said it looked like sinusitis, but to give it till Wednesday before starting antibiotic. My son continues to fight the fever (we use tylenol or advil every 4 hours) and we can get it to 99.9 but if we waiver, it goes back up. He is congested, has a headache, no appetite and if he eats once a day that s a lot, now he says he has a pain from his groined area up to his stomach. What should I do?