Here is info for you -
What exactly is thishormonal contraceptive? Much like the Pill, it prevents ovulation and makes the cervix and uterine lining hostile to sperm and fertilized eggs. It uses a synthetic version of the hormone progesterone to achieve these results. Unlike the Pill, your physician will give you a shot, usually in the arm or buttocks.
If Depo-Provera shots are received on a recommended basis, pregnancy is highly unlikely. While the contraceptive has the power to prevent conception up to 14 weeks, the injections are usually given every 12 weeks to ensure that there is no gap in the effectiveness of the birth control between shots. When such a schedule is maintained, pregnancy while on Depo-Provera is extremely rare. Those 1% women probably end up with an ectopic pregnancy.
Suggest you visit a doctor and have yourself thoroughly examined. Good luck