I've been getting the injection since 2003. For the first 3 months I had spotting the whole time, but from the second time on I didn't get AF for the whole 3 months. That's how I knew I was due again. AF would return.
Both pregnancies since were planned. DD2 took 4 months - 7 since my last needle - & this pregnancy took 7 months - 10 months since the last needle to concieve.
I think the longer you are on it, the more it builds up in your system & the longer takes to wear off completely. I have put on a bit of weight. Only about 10 kgs, but slowly over the years, so it probably doesn't have much to do with the needle. Just me getting older I guess. Having babies doesn't really help either!
It can be used when breast feeding too. Some people have alot of problems with it, but for me there's nothing else. I love it.