Pregnancy after plan B?

I took the morning after pill a day and a half after unprotected sex which was also 2 days before my expected period which was Wednesday, March 2. I took a pregnancy test the following Thursday, the 10th at midnight after drinking a bottle of water and it came back negative. I still have not had it yet. I have very mild cramping when it is usually more painful and my period always came at the same time every month. Has anyone had an experience like this? Can plan B push back your period more than 2 weeks or cause a false negative on a pregnancy test?

Thank you