Ideally with any new contraceptive you should use other methods (condoms) for the first 14 days. It is possible to become pregnant. You need to wait a few weeks then do a home pregnancy test.
the depo is effetcive as soon as you have it, it takes effect immediately
I don't think you could be preg. Depo is very very affective, but if u do want to get preg then u should get off depo cause it messes u up. I was on depo for a year and a couple of months and I didn't get my period at all and now I. Off depo ad still haven't gotten my period. Me and my boy friend are TTC but I don't think I can cause I haven't had a period. So if ur planning kids in the future should get off depo and use a diff kind of birth control