Greetings ! i am a 30 year old married woman, just delivered a baby before 7 months. i am having backpain for more than 15 years since i am obes?

Swim: If you have access to a swimming pool, swimming can safely improve many types of back pain as well as weight loss.

Get evaluated: You should get evaluated. An x- ray or even an MRI to make a diagnosis. Likely mechanical. Exercise especially abdominal strengthening post delivery. Weight loss. Watch posture.

Unsure: I am not sure what to tell you. I think you are on the right path with your weight. Remember that carrying your baby is stress on your back also. I don't know if you are breast feeding. Sounds like you need to be worked up by a doctor.