Love your pediatrician or not, if it was my kid, and I was worried I would be at the hospital. Swollen lymphnodes are not nothing. The one in the chest is good size, but it sounds like the cheek one isn't too big -- a stranger looking at him isn't going to notice it right away, right? He has had it for the entire 2 and 1/2 months since Christmas -- it didn't go away and come back?
I might call the pediatricans office now before it gets to be really late. Tell the you are worried and thinking of going to the ER and see what they say. At least that way youll be on their radar screen for tomorrow, and they might be able to tell you something that will help you sleep a little easier tonight.
EDIT -- I guess I am a minority here, but some times it isn't nothing. My husband had a bruise from a christmas basketball game. It didn't heal so he finally went to the doctor. He even was in the hospital because of it. They sent him home to come in at 10AM the next morning -- 2AM -- for want of 8 hours -- he had a brain hemorage -- lost his spleen, had brain surgery, spent 11 days in a coma, had to learn to walk all over again. It wasn't nothing, and it started with just a bruise that wouldn't heal. After an experience like that, I call when I am scared with things I don't understand.
You need more information, and calling could help.