Could I be pregnant?

About a month ago I've had sex with 2 different boys both without a condom within a 2 days separation they both said they didn't ejaculate in me but I didn't get my period for the rest of the 3 weeks left in the month & now we are almost one week into this one. I smoke weed everyday & I took a pregnancy test & it came out negative but I still haven't received my period yet.. can I be pregnant?