Hi Barbara,
My son just had the same surgery this past spring. He woke up during the night as well, he totally refused the pain meds so he was just on Tylenol. What I had to do was no matter what I thought he needed a dose every 4 hours, if I let it go longer he would end up in pain and then it would take even longer to get some relief. Then on day 8 or 9 BAM, really bad pain. I called the ENT and they said it is "referred" pain and it is very common, mostly in the jaw & ears, but in a 4 year old, pain is pain. I would say w/ several ups and downs, my son took every bit of the 2 weeks to recover and go back to "normal" and sleeping peacefully at night.
As for infection, I would be surprised if your son isnt already on an antibiotic, I think they send you home w/ a RX for 2 weeks worth to fend off any potential for infection.
So in a nutshell here is my advice. Call the DR. to set your mind at ease, that is what they are there for...but dont jump the gun on it being anything serious!