Me and my girlfriend had unprotected sex around new years. I am positive I didnt cum but just in case the next morning I had her take Plan B. 3 or 4 days later she had a light period. Then about two weeks later around January 16-20 she had a heavier period. In February we are now on the 20th and she has not had her period for this month. She took a pregnancy test on the 20th and it was negative. Not sure what is going on here. We are both very confused.
A VERY common side effect of plan b is that her next FEW cycles can be early or late and heavier or lighter than normal.
Again, her period is likely to be "off." It should return to normal in a few months.
It is unlikely that she is pregnant, taking Plan B within 72 hours.
Hope it helps.