Suggest Remedy For Recurring Fever After Tonsillectomy

Hi My son had a tonsillectomy just over 2 weeks ago. He then had a bleed a week after his surgery and had to go back and have it stopped under anaesthetic. He developed a fever on Tuesday, was seen by a GP Wednesday and we were sent to the emergency department. They checked his urine and did a chest X-ray and all looked ok and he was diagnosed with a viral infection. On the Thursday he was still very unwell lethargic and with high temps. I took him to his Gp again who commenced him on amoxicillin, he thought his throat looked infected. By Friday his condition hadn't changed and he still had high temps. I took him
Back to the Gp who changed the abs to Aumentin Duo Forte. This morning he had improved although in the last two hours his temp has slowly been rising again. It got to 38.3 and I gave Panadol and it has come down to 37.3 He is not eating a lot and is in a lot of pain. Wondering what your advice would be with the current temp, do I just need to give the new antibiotics longer to work?