I have burning radiating pain under left breast. ruled out cardiac & dx costochondritis. this has been going on over 2 years. is it normally that long?

No: I would be looking for other explanations. Perhaps even post herpetic zoster (shingles)? Sometimes there is no rash. I'd also look for problems along the upper spine. Besides your regular doctor you might also see what acupuncture or manipulation would do but I think you are right to ask for another explanation. Costo-chondritis I would expect to get better with care and time.