This is an edit of a post I made two years ago. I had a hysterectomy (for a baseball-sized fibroid) eight months after I wrote it. It turned out that my womb could never have produced a child; muscle tissue and lining tissue were intermingled, rather than being in layers as they ought to have been.
My periods were nearly always regular as clockwork (though beginning in my late thirties I tended to skip a period in the hottest days of summer). So I'm a counterexample there.
On the other hand, I always had ridiculously heavy periods (an "overnight" pad would last me two hours at most). My periods were agonizingly painful (enough so that all I could do was stay in bed for a week when they hit), and the pain grew even worse as I grew older, but no doctor ever found evidence of endometriosis. I also have a long history of UTIs, cystitis, pyelonephritis, and yeast infections.
Note, however, that I've never thought that any of it had anything to do with CFS, as I'm a DES daughter, and the heavy periods and pain were present from menarche, a decade before I got CFS.