Ok, with encouragement from Mamafoof, I will post my sorry story, if only because it contains a tiny nugget of information that might help.
You may remember that I have made (possibly patronising-sounding) references to having had a "contraceptive injection" in the past. I live in Germany and what I was given is sold under the name Sayana here. I had googled it before and come to the conclusion that it wasn't Depo, but started googling again after reading the most recent "depo is the most evil stuff ever" thread on here and realised it was. (For anyone who hasn't read any of those threads, they are full of people saying they took five years to conceive after stopping depo, depo should only be given to women who do not plan to have any more kids, etc. The German forums said basically the same.)
Fortunately I got the new version of depo which has a third less hormone in. My gynaecologist said it would be okay when breastfeeding and that it was 100% effective. To be fair, she must have hinted that it might take a while for menstruation to return, because she said something about going on the pill for a month as a kick start, but at the time I wasn't in a rush to get pregnant again.
I'm just feeling frustrated and impatient. I started spotting again yesterday, but it's pretty much gone now, exactly like the last bout 8 weeks ago. I assume this is breakthrough bleeding and I haven't ovulated. My temps are hovering around 36.4-36.5 and haven't dropped and also the bleeding was so light. I guess there's nothing I can do but wait and chart to see when I might finally ovulate.
The nugget of information, Mamafoof, if you're still reading, was that some women have low progesterone levels after being on depo and cannot support a pregnancy, but that this is easily rectified by progesterone supplements, which I guess you take from ovulation. I can't imagine you'll need them, though, I think ladygg is right and you'll be pregnant again in no time.