If it were me, I'd probably wait until it'd been about 14 days since my last test, and test again. I suppose you could be pregnant, the crampiness can be a symptom, but it can also just be that your cycle is totally out of whack now, thanks to the depo shot (I've heard MANY women complain that their cycles were completely off track for quite awhile after having the shot). If the pain continues, I would definitely see a doctor though--you shouldn't be having that much pain, whether or not your pregnant...
Good luck!!
Whiskers