Edited by CaliMommie - 7/30/13 at 10:49pm
What tests have you used? Have you tested again lately with a sensitive digi? Unless the faint lines you saw were greyish and not colored, showed up after the allotted time window, or were so faint they were squinters, I'd say a line is a line! It's possible you had an early loss which gave you some BFP's and now your levels are low enough that you're getting BFN's and will bleed soon. I know there are some uncommon cases where the products of conception are reabsorbed by the body and no bleeding occurs until after the next ovulation, which could be delayed due to the m/c.
If you're feeling unsure of the BFP's, then major stress is absolutely a possible cause of very delayed O and AF. Have you been getting patches of fertile CF over and over again? This could point to your body trying to O several times and not succeeding. Another possibility is a corpus luteum cyst. They are benign and usually resolve themselves within a few weeks at which point you would bleed. They are not common, but it is thought that every woman will have at least one in her menstruating career.
But if you're pretty sure of those BFP's, then I would suggest a quantitative blood test. If your levels are still slightly elevated (above 5), but not high enough to test positive on an HPT (25) that would point to an early loss and you'd have your answer. Otherwise, it sounds like your body needs some time to regulate and will O and/or bleed when it is ready.
Good luck and keep us posted!