I've been on ritalin (methylphenidate) for a year, but I'm now suffering from frequent chest pains. Should I stop taking ritalin (methylphenidate)?

Yes. The development of any chest pain requires proper evaluation by a physician. While it may be related to a minor non -serious issue, Ritalin (methylphenidate) is a known cardiac stimulant. It can provoke extra heart beats, elevate blood pressure and in some instances even provoke a heart attack.
Probably. Consult with your doctor to possibly switch you to a different add/adhd medication.