I am on provera as well - my doctor told me that it was to "re-set" your system so that the following month, you might start ovulating again. BUT - BEFORE YOU START EACH PROVERA TREATMENT (5-10 days), TAKE A PREGNANCY TEST. My doctor didn't tell me this, but I've been researching and everything says that Provera can be very damaging if you take it without knowing you are already pregnant. So basically the idea is to get your system to start ovulating naturally. In general, you can know that if you're not getting your period, then your progesterone levels are not normal and you are likely not ovulating. The provera is a synthetic progesterone that causes your period to begin, and might get your hormone levels "jumpstarted" to get moving again in the right pattern.
As far as the infertility is concerned, everything I read says that once your body gets back to ovulating, you should be able to concieve... but of course every individual is going to be unique, and there's no way for me to tell you whether or not you're infertile. I'm concerned about it too. I'm only 24 and have never had issues with regular periods before now... my doctor says the hormone issue should work itself out and that it could be due to stress or any other number of things.
Hope this helps!!!