Hello Danielle,
Depo provera contains medroxyprogesterone which is a long acting but reversible hormonal contraceptive. When you stop taking the depo shots, it takes some time for your periods and ovulation (release of eggs by ovary) to return and in some women it has been reported to take at least 12-18 months for the periods to return.
Since you have stopped taking the shots in Feb 2011, hence you will take some time for the periods to return. However sometimes ovulation can return prior to periods and in that case, having an unprotected intercourse increases chances of pregnancy. I suggest you to get your serum pregnancy test done which measures the amount of HCG in blood. HCG is a hormone produced during pregnancy. Its levels will confirm the status of pregnancy.
I hope this answer is beneficial for you. Wishing you good health. Regards.