Levonorgestrel
"okay ladies, just calm down. heres my experience, I've taken Plan B about 5-6 times in my life and I've never had this happen till now. I took plan B on the sunday of my first sugar pill, I had unprotected sex the night before with some strange man and a friend of mine. not knowing him I certainly didn't want his baby so I decided I'd take plan b just to be safe. ... tuesday came and I didn't get my period...5 days later I FINALLY got my period! most nerve wracking 5 days ever.  I actually went and bought a pregnancy test on thursday and told myself that if i didn't wake up with a period on friday, id take the test. thank god i didn't have to take that test bc aunt flow finally made it and I welcomed her with open arms. .. it'll come, just wait"