Day 12 or Day 15?? Help!!

My charting over the last 2 months is driving me NUTS!

Anyway, what has happened this month:

I started doing OPKs at day 10 and continued through to day 14. They were all neg, but the line came up weakly in all cases. But the one on day 12 was more positive than the rest, quite a bit darker but still not a dark as the control line. So I was fairly happy to call it positive. I kept temping and this morning FF has given me a hashed coverline with day 12 as O day. But I am fairly sure I actually Oed on day 15, it corresponds with my other signs and out of curiosity I took all the OPKs out of FF (because technically they were all neg anyway) and it then gave me a solid coverline with O on day 15.

Now I guess it doesn't really matter because we still timed BDing well anyway, but the OPKs are driving my insane. I've been doing them for 4 months now, and they worked the first month and haven't worked since. And I've had 2 miscarriages/chemical pregs, the last one the cycle before last, the first one the month that the OPKs worked. Also, since the last m/c I've had a 28 day cycle instead of my regular 24 day one, and I'm pretty sure this one is going to be longer than 24 days too. I'm so confused!! I wouldn't have thought that a m/c as early as mine would throw your cycle out this much??

So I was wondering what you experts think? Did I O on day 12 or day 15? Is it possible to get a positive OPK 3 days before ovulation? Or should I call the OPK neg, whick according to the kit instructions it really was?? Any other helpful comments? LOL

TIA

FF only thinks you ovulated onday 12 so it may well have been day 15!!
OPK never worked for me

I threw out my OPK results last cycle for the same reason - I never get a clear +ve, Ff gave me a dotted line until I threw out the OPK result, then gave me a solid coverline for a day later. Turns out it was probably right, as AF turned up on 14dpo right on schedule.