Hello. Welcome to hcm.
Your condition might be due to congenital mal development of pectoral muscle which will be from birth or weakness in nerve
supply which can occur after trauma. Trauma can be to arm,back or head. There no need to worry about excess estrogen
or tissue as every persons problem is unique and only a qualified doctor can diagonise the condition.
I advice you to see your doctor who after examining you,wil also order for tests depending on site and cause of pathology and will be treated accodingly.
All the best