If you want to have a baby soon, don't get another depo shot! I read somewhere you need to be off the shot for something like a year to a year and a half if you want to try to conceive. (it is possible to get pregnant while on it, of course, but most women don't get their periods until something like 10 months after their last shot has run out.)
You should really talk to your doctor.
a pregnnacy test is the way someone would know they are pregnant while on the depo. if you want to have a baby then simply when you go to the doctors...tell them so.
and since you want another baby....why are you questioning what "birthcontrol pill...to use?" that would prevent you from getting pregnant