The birth control shot is an injection of a hormone that prevents unwanted pregnancy. Each shot prevents pregnancy for three months.
As you stated that you have taken it only on March 2013 and never again. By your explanation you might be pregnant as you had sex the day after your ovulation day and also your partner has ejaculated inside you.
You can clarify your doubts by pregnancy tests the presence of the pregnancy hormone, human chorionic gonadotrophin (HCG) in your urine.
After you conceive (when the sperm fertilizes the egg), your body begins to produce HCG. Around two weeks after you conceive, there’s enough HCG for most pregnancy tests to detect it.