Ok so I had sex a few days after my period. He pulled out but I took plan b just to be safe. I experienced spotting during my fertility window (day 17-19 of my cycle). Now I'm at day 37 of my cycle and no period. My cycle has been regular at 35 days and I have been experiencing cramping like I do before my period but it is very mild. I took a pregnancy test on day 25 or 26 and it came back negative. What are the chances that I could be pregnant? Or is this all in my head? Please help.

*UPDATE* just took another pregnancy test and got "not pregnant".