It has been 1 year and 5 months since I broke my left elbow something FIERCE (2 plates+12 screws+2 pins+2wires holding my arm together) and I still have wicked pain! Every day since I broke it, I have pain...EVERY.SINGLE.DAY!!! My orthopedic surgeon told me it would take around 2 years before I could no longer be aware of it and to expect to have mild pain for quite some time after...my physical therapist said to give it more like 5 years till I was un-aware of it any longer.
Not sure the extent of your son's break but my advice would be to take him in to have another x-ray and just get it looked at, it can't hurt right? But other than that, I say that him having some pain sounds normal to me...it's only been a year and breaks are kind of a big deal!
For peace of mind, take him in but I bet he is gonna be OK.