Pain meds never cured anything - they are coping drugs that lose their effectiveness, as you are learning.
If you want to actually take something that could cure your endometriosis, you are going to have to go back to a non-synthetic herb. You need to buy one that says it's organic and cold pressed. Amazon lets users rate things, so choose one that gets 5 stars.
Nigella sativa is an herb. You can buy it in oil form or in a pill form on line, such as from Amazon. It has been used since ancient times. Pharmaceutical companies have tried to put a patent on it but thankfully have not been allowed because it is natural and not synthetic. Look it up on line to see how people are using it for your condition. It often involves putting the oil into good quality (real) honey. Other times you can put it in juice.
It has a strong herbal taste, but it's kind of like oregano. Mixed as above or taken as a pill it is easy to take. Better than pain and disease. While it is curing your endometriosis it is also dispatching of any cancer cells roaming around, and other inflammation, etc. It is a wonder herb. I take it every day.
Pharmaceutical companies are trying to take our rights to herbs and supplements away. Get involved politically and let your senators and congress know you don't want your rights taken away by pharmaceutical companies.
You are right this is very rare and only something I heard about a couple of years ago. I was actually a non believer until I spoke to someone in the Endometriosis world for the last 30yrs.
What you need to do is find yourself an Endo surgeon. The disease needs to be properly removed if not it will continue to grow and cause pain.
I can help you with this, please let me know where abouts you live and I can give you some names of surgeons that would know what to do.
Thanks,