I have pectus excavatum and i have low tolerance for exercise because of it. can i do sports like track and field or should i see my doctor first?

See a doctor first: You have low tolerance to exercise which could be due to structural limitation to your lung capacity or cardiac capacity. A professional evaluation may help identify your limitations.

If you are having: Health issues that impact your ability to exercise you may wish to see a sports medicine doctor to get cleared first.

You can do sports: You are fine to do aerobic activities and can probably improve your endurance. Indications for repair of pectus excavatum are a severe deformity (Haller >3.2) and cardiorespiratory symptoms, like yours. You should see a doctor and have studies ordered to work this up (chest CT, ECHO, PFT's), as this condition is likely to get worse with pubertal growth. You may benefit from having this fixed.