I tend to have brown spotting three to four days prior to my period. It does not happen every month. According to my temp charts and OPK tests, I am ovulating regularly at approx cd13-14 and my cycles are 27 to 28 days. What could the potential reasons be for this spotting? Is it normal or could there be a progesterone problem or luteal phase issue? I was told I don't have the signs for edometriosis. Could it be late implantation spotting, but it wasn't able to implant properly?
It's probably some lining of your womb that required a certain threshold to maintain, but sloughed before the "rest" of your period when the hormones began to fall ... with the rest of the menstrual tissue following like normal. It is possible this could represent a luteal phase defect, but the fact that you're so cyclic speaks against that. A progesterone test day 21 to 22 can tell you whether you ovulated well. An endometrial biopsy a week later can tell whether the rest of your endometrium (lining) is in sync with the ups and downs of your cyclic hormones.
Endometriosis has nothing to do with this. I don't believe in implantation bleeding, especially bleeding that's cyclic.