I've had the shot. I was supposed to return to get the shot April 16th. I had unprotected sex on the 28th of April. Can I be pregnant?

Pregnancy unlikely. The protection of a Depo-Provera shot does not vanish in 12 days, but lessens over time. However, one can do a pregnancy test. A urine pregnancy test, done correctly, gives a reliable result 3 weeks after sex (3 weeks after when conception might have occurred). If done sooner, a positive result is likely real, but a negative result may be due to testing too soon, and thus lead to a repeat test.