Hi,
Sorry you're going through this.
Here is a link to a page that presents your options so you can read about them. I think a strong progestogen treatment would be better than putting any extra oestrogen in your body e.g. with the combined pill.
http://endometriosis.org/treatment.html
This page has a variety of treatments explained, including natural and lifestyle approaches you can take to alleviate symptoms.
I hope this helps.
I know a lot of women with moderate-severe endo seem to be on Zoladex which I believe puts the body in a state of menopause, which is reveresed when treatment stops. While in a state of menopause, endo shrinks and doesn't continue to form, which slows the growth rate down after treatment and gives (hopefully) a period of time without problems - though this varies from woman to woman. The side effects are, of course, like that of the menopause, but many women who have terrible pain and other symptoms due to endo are willing to go through these for some relief afterwards.
I hope you can find something that works for you.