They are pretty effective, the plan B pills. I think you've been lucky to not have your period and cycle affected when you've taken it in the past. For most people, it messes them up for 2 to 3 months. It's a big dose of hormones so it mixes in with your regular hormones and can cause all sorts of things like bleeding when you're not supposed to, not bleeding when you want to, etc. My guess is you are not pregnant. 2.5 weeks after the 4th of February, you could take a test and find out. But really, don't think so. It also matters where you were in your cycle--- when was the first day of your last period, for example?