How long should a fever last after starting antibiotcs

Patient: My 6 year old son woke up with a fever of 104.6 thursday morning about 2am. My husband took him to the doc Thursday afternoon, they took blood and said his has a bacteria infection and gave him Cephalexin. His first dose of that was about three Thursday afternoon and he takes it evey 8 hours. Well it is saturday night and he still has a very high fever he woke up from sleeping this afternoon with a fever of 105.3 I can get it down to about 101 with tylenol but it just comes back in hours. And I also notice today his tonsils are very swollen. So I’m wondering should I be taking him back to the doc sence his fever still won’t go away or does it just take this long for antibiotics to kick in?

Doctor: