Bleeding, paining nipples while exercies

Patient: I am a male 38 years old, I was lost almost 10 killos, still chubby, goes to the gym for workout, but every time he exercises especially when, RUNNING , JOGGING carrying wight, MY nipples bleed and hurt so much… pleas help me find an answer fot this, what could be the cause and how to deal with it. could it be dangerous?please i need an answer as soon as possible, incase we should see a which doctor..thank you very much

Symptoms: Hard pain in nipples