Took plan b but feel pregnant?

took plan b five days after , that was 3 days ago, no bleeding or anything but extreemely naseus ( for a week now) cramping. I didn;t have this the other timei took one (didnt need to though i found out later on missed calculated dates) didn;t have any side effects with the same pill last time... myPeriod due on the 1st i took early detection test late this morning was negative im going try again in two days. But do you think i could be pregnant?