I had unprotected sex 2 days after my period. We had a mistake and I was worried, so I took Plan B because I am not on birth control. A week later I got my period. Now it is right around the time that I should get it, but I haven't. Also I took a pregency test 2 days ago and it was negative. Am I OK? Will I not get my period because I got it early.

Taking it can effect your cycle and period. Along with varoius other side effects.

But it is also only effective in 7 out of 8 times so it is far from 100 percent effective.

What is Plan B? (http://www.go2planb.com/ForConsumers/AboutPlanB/WhatisPlanB.aspx)

The morning pill usually messes up periods. When I first took it I was bleeding heavily and after it stopped I had no period after a month maybe 2. It's quite common.