Well, it's not possible to fall pregnant on an anovulatory cycle as there is no egg to fertilise.
Not all women ovulate on day 14; that is a total myth. Women can ovulate earlier or later than day 14, or not at all.
Best advice is lots of sex. Every second day or so or more if you fancy it!
If you wish to use OPK's perhaps start using them earlier in your cycle, and keep using them until you record a +ve OPK. I'd recommend charting as well, which would show with a sustained temperature rise if you have ovulated in any one cycle.
(I have a long cycle and didn't get an OPK some months until day 18 or 19) but one of the months I did get pregnant I didn't get a +ve on the OPK at all.
OPK can be a bit hit and miss IME.