OPK confusion

[mamma2016]

Hello, looking for some advice. We have one lovely 3 year old, conceived using OPKs. Successfully conceived again using OPKs in Nov but went on to have MMC. Keen to start TTC again as we put it on hold during lockdown due to uncertainties with work and other anxieties.
I've used OPKs to avoid pregnancy over the last three months. This month, started getting faint lines on days 12 and 13, seemed early for me to ovulate as usually around day 18. Then had several negatives. Today, day 21, felt a sharp twinge from left ovary (but maybe it was just wind )

Did a test this PM which appeared positive. Then another one hour later and no line at all. No line yesterday either. Could this be a false positive or was surge so short it came and went in a blink?

This is only my first month TTC, but I had similar this cycle - my surge seemed to come out of nowhere, I got a dark line around midday, and then by 3pm it was fading again, but still a lot darker than I would usually get. By the next morning it was back to faint again, and the day before I got the peak it was just the usual faint line. I've looked into it and apparently some women can get a very short surge which makes it easy to miss x

Thanks for your reply. Good luck TTC! X