Enormous back pain while stretching?

Patient: I have suffered from a pars fracture and a herniated disc for the past 2 years. I recently switched doctors and was told that because of my age (17 years), I would heal quickly and should resume activities and begin to stretch and strengthen my core. I am afraid I have overdone it, and now experience enormous pain when bending and stretching. What steps do I take at this time?

Doctor: