Plan B One Step

I took Plan B yesterday, any my boyfriend SWEARS he didn't ejactulate inside of me but we did it without a condom and he said he would feel more comfortable if I took it. I've heard rumors that if you took Plan B and you weigh over 150 it doesn't work. I'm ~170 but I still took it to be safe. I woke up today with cramps (just like when I have my period). Is that a conformation that it worked on me? Is there really any way to tell if it did? 😕