What Causes Recurring Fever And Headaches Despite Taking Antibiotics?

I have been sick on and off since oct 31. Fever, headache, crud in general. Three rounds of antibiotics, shots, etc. I have never been sick so much. I m 61, female, healthy, retired 2 yrs ago from teaching but went back this year. DHR also placed 2 grands with us on sept 22 (9 mos and a 6 yr old). So I ve had a lot going on. But my question today is why does my fever of 101.4 come back around 3:45 yesterday and today? Thank you