I was put on ortho novum 7/7/7 when I was 18 because of painful heavy periods. Unfortunately, I gained weight, but I think it was more because I just started college at teh same time because I have been off the pill for a few years and haven't lost any weight. It definitely helped by making my periods almost pain free and much lighter. Unfortunately, the reason for my pain was caused by fibroids which I later learned probably grew from the estrogen in the pill. I wish I had investigated the reason for my painful periods before going on the pill. I could have had the fibroids removed which were the problem and not needed to go on the pill at all. You might want to look further into the cause of the pain. Have you had an ultrasound? It won't diagnose endo but can rule out other possible causes of pain.
But anyways, overall, if you don't have fibroids, the pill will probably make you feel a whole lot less pain.
Take care!
Stacy