Am I pregnant????

OK so my period is late and on the third day after the sex I tried to take a plan b pill but I'm not sure if it worked. I haven't gotten my period but I am spotting like pink I guess. Sometimes I won't see the pink for hours then sometimes when I go to the restroom when I wipe it comes out pink. I was thinking its my period but I doubt it. I usually have heavy periods. I took a test but it came out negative. Help I'm kind of freaking out. I can't stop worrying about it.