The drug information for Focalin indicates that chest pain, palpitations, and anxiety are all possible side effects of the medication. This is definitely something that you need to discuss with your doctor. Although your son has been taking the medication without adverse effects for a few years, the medication is still relatively new, and the long-term effects aren't well-defined. Tell your son's doctor about what he's experiencing and then go from there.
Best of luck,
Casey