Hi Dollysgirl, I just wanted to add my experience here too.
I started the depo in March 2005 and continued to have it until december 2007. We got married in Jan 2008 and wanted to start a family pretty much right away. I didn't have a period until December 2008 and this was very light spotting (not what my periods were like before depo). It took until March/April 2010 for my cycle to become anythign like regular, but this was anything between 32 and 45 days. I went to my GP and had hormone tests, these showed I had PCOS (although I'm not convinced this is correct and the imbalance was still being cause by the Depo). I then started doing home ovulation tests (I did 100's because my cycle was so irregular) and not one showed I was ovulating. I had a few 21 day tests, but because my cycle was so irregular they were never accurate. As a result of my 100's of -ve ovulation tests and the 21 day tests we were referred to the fertility clinic. Felt like a lifetime for the appointment to come through, eventually it did 26th August 2010. I carried on as normal with the ovulation tests and when I got to day 33+ of my "cycle" would do a pregnancy test just in case. They were always negative in July I said I wouldn't do anymore as it was upsetting.
Then the day before our appointment at the fertility clinic I was speaking to my friend who was pregnant and I happend to mention I felt like my period had been due for over a week, emotional, tired, aching boobs etc. She said to do a test, just so I knew for sure before my appointment. She still had one left. I took it to the loos at work because i waqs certain it would be negative. It was positive :o! Fertility clinic confirmed the next day I was 6 weeks. And confirmed it was quite a regular occurance for people to turn up at the first appointment pregnant.
I'm now 32 weeks with our much wanted and much loved DS. I still am shocked that I am actually pregnent, because we weren't even "trying" very hard because I thought I wasn't ovulating.
I now know that the Depo isn't offered to anyone looking to start a family within 5 years and I've convinced friends who used it to change to something else (most chose the implant), feelign guilty because I recommended it to so many as I thought it was brilliant when I was on it.
I hope my story helps you in someway and lets you know you are not alone in the way you are feeling about it all. I wish you all the very best.