Who/what is telling you you're "due" to ovulate a certain day? An app?
Are you using the "low/high/peak" from a fertility monitor or an app?
Please just use the OPK in terms of it being positive or not and nothing to do with low/high. If it's peak, the odds are good that it was a true peak. There's no "baselines" or anything like that, if the hormone reaches a certain concentration you'll get a positive.
The rate at which the test goes negative does NOT tell you if you ovulated or not. The surge and ovulation are not directly linked the way people think of them. You can have a positive OPK still after ovulation and a test that's gone negative prior to O. The tests merely register the hormone that signals your body to ovulate soon, and NOT the ovulation itself which your body sort of does on its own timeline. But after the signal is received it just takes however long for your body to clear the hormone. In most cases you will ovulate 24-36 hours, and less often as long as 48-72 hours after your first positive OPK regardless of when or IF the test has gone negative.
I don't like every other day sex (I can explain why if you like) But the important thing is that now you've gotten the peak, you need to be in with as many attempts as possible, at least three if you can. When is the last time you had an attempt??? Since you just got a peak you need to have attempts now now now!
Ovulation pains do not predict ovulation. You can get them before, during, and after O and they trick people constantly into having attempts at the wrong time and stopping attempts too soon. And there is no "normal" in O pains - you can have them in one pattern (or not at all) for a long time, and then the pattern changes, and it's all normal. So it really doesn't matter what happened in the past as it would probably be different now anyway.