Hi. So, you are probably fine. Plan B does work really well when taken within 3 days of your period. But the downside of taking it is that it is a huge dose of hormones (which is how it works) and those hormones are then in your system. This causes things like irregular bleeding and it can last up to three months. Most likely this is what happened here. I would think this is a normal pattern after taking plan B sweetie. You can double check if you think it is necessary at any point taking a pregnancy test when it has been two and a half weeks after you had sex. That's soon, right? But I would be shocked if you were pregnant. :>)