Kind of missing af

My periods have been normal up until I had gotten the depo shot last April. I only got one shot because I found out you wouldn't be able to conceive for up to a year after you stop getting the shot. Last December I started getting regular periods and I would get them at the end of every month. I had my normal period March 28th and it lasted it's normal 4-6 days. And then on April 11th I was sexually active and I had started bleeding excessively to the point where I think it was my period. Well it is now May 20th and I still have not gotten a period since then. What could this mean???