Hello, I Have Been On The Depo Shot For 11

Hello, I have been on the Depo shot for 11 months and was told to come to my 5th session between Dec. 10 to Dec. 14. I however was unable to get my shot at that time and during those days I had unprotected sex. I went in to get the shot on the 18. I'm experienceing symptoms that I didn't have when I took previous shots. Could I be pregnant? I took a pregnancy test and it came out negative but I know they may not be accurate.