OPK help/When do I ovulate

Emily

I know I should wait a couple days to see if it gets darker, but I’ve had some issues getting a positive ovulation test. My fertile window started yesterday, and I’m supposed to ovulate on the 31st, but I don’t see my ovulation tests getting any darker... but this morning I started having EWCM. I’ve tested for a couple months now but this is my first month using this app, and I’ve yet to see a positive result. I’m on day 16 of this cycle. If I have EWCM should I assume I’m fertile and should start BD? Do some people never get positives because they don’t produce has much LH? Help!