C.M.
I am actually in the middle of the same thing with my two year old son. He was diagnosed with a sinus infection and started meds yesterday. My doctor said to call him back Friday morning (tomorrow) if I felt he was not much better and he would prescribe something stronger. He said he didn't want him to go into the weekend getting sicker. Well, the amoxicillin isn't cutting it( it never does) so I will be calling in the morning.
I have never heard of that happening and you might consider a new dr. if they are THAT unhelpful. I hope your sweet boy feels much better soon!