I suppose you're not on Provera now? If not, then there is a possibility of getting PG.
From what I gather, you had your last period over a year ago? There must be a reason for this. Have you been to see the doctor? If not, then please make an appointment, as this may affect your future fertility!
O.K, in response to your question about how long before taking a hpt, normally I'd say about 2 days before your period is due, but in your case you don't know if you're going to even get a period, so I'd say: if you had unprotected sex 2 days ago, then you'll have to wait for at least 3 weeks. (taking into account that this could be the beginning of your cycle)
If you get a negative result, repeat the test on the 4th week, and on the 5th. That should cover it. Again, I'm advising you as if you had a normal 28-30 day cycle....
Another thing...if you're not menstruating, you may not be ovulating, but then again, you could be, so please go to the doctor and clear this up.
"I am not young enough to know everything."
- Oscar Wilde (1854-1900)