Am i pregnant! emergency!?

I cant get pregnant now.. big mistake. Supposed to have started period on wed..its not saturday night no period. But i read it could be late due to eating and stress.. i had midterms last week and was stressed about those plus, not purposely but i havent been eating as much. When and should i take a pregnancy test? No tender , but stuffy nose today? I took the plan b last (fri) night and this morning... HELP!:( p.s. I had last tuesday..