My period usually comes around the 19/20 and last month, i took a Plan B pill and it affected my period, causing it to occur about a few days later than normal. This month, everything has been normal, except for my period and it is the 23rd already. But for some reason, <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Eve</a> thinks that my period will begin in 2 days? Please help. Why is my period starting later?