Help help pregnancy?

I’m about to sound crazy so be warned. I had sex on September 26. I was on the pill until October 6th. I went in to the gynecologist to switch to the shot on October 6 and this was while on the second day of my period. They tested me for pregnancy while on the second day of my period (withdrawal bleed) and it probably was negative because they gave me the shot after that but I’m nervous because it hadn’t been 2 weeks since the time I had sex, and the time I got tested for pregnancy. Could there be a chance that I’m pregnant? I mean we used condoms and I was on be pill, it’s just that he tried to put the USED condom back on without me knowing and I don’t know if some semen could have slipped out.