Hello My Son Is 1 Year And 2 Months Old,

Hello
My son is 1 year and 2 months old, he has been having for 4 days today starting with 38.7c 1st day and reaching 40.5c at the 2nd day and then between 38 and 39. My doctor 1st diagnosed it as teething but then when i visited him again he told me that he is doubting its a roseola and that some rashes might appear after the fever is gone.
Its also worth noting that he checked his throat and he said it was a bit inflammed and gave him an anti-biotic.
Also he doesnt have a cold or flu or severe diarrhea, only runny stool that today looked orange and i thought it had blood so i sent it to the lab for diagnosis but came out normal with no blood but with mucus and puss only.
Im so worried as the fever is not ending and im not sure im giving him the right medication! What could it be? Please help!
Thanks