Could i be pregnant?

ok well i dont think i could be since id be already not having my period. But here goes, I didnt have but i was messing around with my boyfriend and im scared he got something on me cause my period was two weeks late. I had sweatpants on and he had boxers. We were just like rubbing. Ive already tooken 3 pregnancy tests and they have all been negative and ive had 4 periods could i still be pregnant? I think i mayy have gotton pregnant on december 17 2007