i was on depo for two years and i then started taking the pill in january 2007. i stoped taking the pill in october 2007 and i got pregnant in december 2007.
so going onto the pill worked for me.
I was on depo for 3 yrs, and luckily got AF the first month off depo.
Personally, I believe if you are having regular periods, you need to buy some ovulation predictor tests, and see if your even ovulating. They're pretty expensive but you get alot of them, just test each day....etc. what the directions say on the box.
That way you'll know if it's because your not ovulating... or whatnot.