When should we consult? Is it normal that tyllenols do not lower the fever? Does gastrointestinal illness give you a fever?

My boy has had an antibiotic for two ear infections and a possible strep throat. He is on Novamoxin. He has been on it since Friday. He also has a stomach bug. Yesterday, after 4 days of antibiotics, his fever spiked to 39. We went to the emergency room. They said it was probably gastro. This morning he woke up with a fever of 40. His fever went down during the day. He was at 37.3 in the morning and at 37.8 at noon. We gave him tyllenols at 4am. He did not want to drink his milk, but he ate a little and drank water. After his afternoon nap, his fever went up to 38.7. We do rectal to him. He is grumpy, he wants to stick a lot, but he urinates, breathes well. His gastro has diminished today, he had 2 stools instead of 6. He has a lot of secretions. He does not want to drink. I don't know what viruses he is fighting anymore. It seems like it's never ending.