Here's what I have to say: GOOD LUCK!!! I was on Depo after having my twins. I had a progressively horrible reaction to it so when it was time to get my 4th shot, I didn't. I had stopped having my period but that was the only "good" side effect. My OB/GYN told me that 20% of the population gets the reactions I was having (well, thanks for the warning doc!!! grrr) After my 4th shot was due and I did not get it, I suspected I would get my period within 2-3 months and then start on the pill. I was due to get that shot in November. In April, I had still not gotten my period. My dr said the soonest he had ever had anyone get pregnant coming off that shot was 9 months after the last shot was due but it was typically closer to 12-18 mos (this was back in 1996). Like I said, my Depo shot was due for November and I did not get it. No period. Nothing. In April, I met a guy and was stupid (unprotected sex). In May (6 mos after shot was due), I took a pregnancy test - AS A JOKE - and it was positive!! I'd had no reason to suspect I was pregnant. No period. No ovulation pains (which are notorious for me). Nothing. And yet, I got pregnant. My daughter was born the end of Jan of 1997, 14 months after my last shot of Depo was due.
I think coming off of Depo is one of the more difficult ones to predict.