sex depo pregnant?

hi! my name is terrylynn! I was wondering if you can help me out. I was on the depo shot (my first shot) I was due to go on the 12 to the 26 but I am not going. I had unprotected sex on January 8th and 9th. my period is 5 days late and for a couple days now I have been having brown spotting. could I be pregnant? I took two pregnancy tests and both came back negative. did I take it to early?