this was my experience, i was 3 weeks late for my period with 6 negative tests but i felt pregnant. Just before my next period was due, i got a positive resullt from from my doctor, which would have made me 8 weeks pregnant by my dates, went for a scan and nothing showed up! had bloods done to confirm i am pregnant... turned out i am only 4-5 weeks gone. So i either ovulate very very late, and got pregnant right before my period was due or i just had a blip on my cycle. But either way, 3 weeks of negative tests... and here i am, 5 weeks pregnant!
You need to temp so you know how long your luteal pahse is and how many days past O you are. That is what says the most! ALso when did you take the OPK? If you take it in the moring you can get a + every time. There is alot of exects to know. If you ahve any hormone problems then temping iwll show it. Look on fertility firend and they ahve a course to teach you and that is the most informative to know where you are in your cycle and it will say when to test. Are you aure you are not anovulatory? Some woman who aren't can also have one or two anovulatory cycles in a year. Anything can elay AF, like sickness, not enopugh sleep and ttc can do it too. Liek the dr says when you stop trying is when it happens:) SO true for many!!!
It may be too soon for the test, try again in a week if you are still late make an appointment. It could be you're pregnant or something else, maybe stress etc keeping your period at bay.
Good Luck!