First of all, no one here is a doctor, so we can't give accurate information. We can only provide what search engines provide. Secondly, this is what your primary care doctor is for.
That out of the way, it could be due to hormones since you're going through puberty, but it's possible that your obesity could also play a role in this. It's possible, but not likely, that your obesity is causing nerve pressure in your breast area, causing that feeling.
Have your parents take you to the doctor, explain your symtpoms, and get an examination with a legitimate diagnosis.