I don't get cramps at all. There is no pain involved with my problem. I'm 32, never had kids.....nothing. The bleeding isn't heavy at all, I use a pad a day, somedays even just a pantyliner. I was reading over the symptoms of endometriosis and the only 2 things that I ever really have as symptoms are lower back pain and the prolonged bleeding.
I had a very similar experience prior to my hysterectomy. I had been having periods lasting 3+ weeks, very heavy and painful, a week or two off and then it would return. Also, they had been irregular all my life. They eventually found I had fibroids, ovarian cysts and endometriosis. Since you don't mention painful periods, just prolonged bleeding, you may have other things goings on.
To help stop the bleeding my doctor had me start a series of shots, Lupron depot or something like that(been years, can't remember). They worked very well. The bleeding stopped, no more cramps but the down side is that brings on menopause. The worst part was the night sweats and severe hot flashes. I couldn't stand that and finally opted for a hysterectomy. The more natural menopause isn't as bad.
I don't know if this is any help but I wish you well and pray you get answers.
For years I had painful, heavy periods that lasted 10-21 days. Multiple doctors said "these things happen;" some mentioned PCOS. After passing out at work from pain and blood loss I was lucky enough to get a doctor who said "endometriosis."
Good news: you won't die of it. (it's uterine tissue which has gotten outside the uterous into the body cavity--but still swells and bleeds each month, causing symptoms of IBS (which I was told was my only problem for 2 decades), back or abdominal pain, weakness, heavy/extended periods, etc.)
Bad news: it can only be diagnosed for certain through laposcopic surgery.
Good news: surgery can VASTLY improve your life (especially if you've had symptoms for a long time)
Bad news: even if you have a pretty good surgeon, it will likely come back. More than most surgeries, it is very important to seek out a specialist in endometriosis, because even a tiny bit of tissue which is not removed will re-grow rapidly in the abdominal cavity.
Bad news: no one knows what happens after menopause (as of 2007, no studies had even been initiated to look into this)
you very well may not have endometriosis--but you should certainly be aware of it, and its symptoms, which can make your life very miserable.
Good luck