Just FYI - an ultrasound can't find endo. You would have to have a laparoscopy for that.
This is a great website http://www.endometriosis.org.au

Perhaps you could have a fibroid or an adhesion? But combined with the heavy periods it could also be endo.

it has been shown that endometriosis can occur at any time between puberty and menopause and that it is frequently found in women who have had children.
I hope you can get some answers. It's not fair to be in such pain and if you can relieve that and the heavy bleeding too, then that would be great.