I took Plan B sometime in June as a "better safe than sorry" method and I got my period a week earlier than I normally do. I keep track of my periods on an app that's pretty accurate. It was the same length as normal but very light. July and August my periods were every 17 days instead of  21. So it was still coming earlier than before after two months of taking plan b. So I was supposed to start my period on 8/14 and I haven't. Is it going back to my normal 21 day period? I took pregnancy test and it came back negative. Just wondering/freaking out.