My Last Unprotected Intercourse Was Last July 4 And Since Then, No Period Up To Now. But All Pregnancy Tests, Both Urine And Serum, Are Negative. Can I Be Pregnant?

I was still on the shot when I had unprotected sex. But since then and since I discontinued the shot, I haven't had intercourse. But since I discontinued the shot, been off of it for about 4 months now, I still don't have my period. I take pregnancy test every week but all are negative. Should I be convinced that I'm certainly not pregnant?