It certainly could be endometriosis. Endo can only definitively be diagnosed by actually looking inside the pelvic cavity. The endo implants generally will not show up on any scan or ultrasound. Since endo creates inflammation it is also accompanied by adhesions. It is possible that the burning pain you were experiencing was the result of the adhesions being stretched during childbirth. Adhesions start out as thin, filmy, mucous-like secretions. But over time they can accummulate and harden to about the consistency of firm rubber cement. So you can imagine what it might feel like if these are attached to any internal organs and then stretched! I have/had endo and it can be extremely painful!

To give you an example of what adhesions can do, I have a friend who has endo that was getting progressively worse and she began developing pain whenever she would sit down. She elected to have surgery and her adhesions were so extensive that they had completely glued her reproductive organs together and also displaced them so that she was actually sitting on an ovary whenever she sat down...OUCH!

Another possibility is an ovarian cyst or uterine fibroids. Fibroids and endo are both conditions that correlate with an excess of estrogen (estrogen dominance), and both can cause pain and excessive bleeding. Both of these can be diagnosed by an ultrasound which is minimally invasive.

I would suggest that you have this checked out since all of these conditions can become progressively worse if not properly diagnosed and treated.