Sooooo... this app

So initially the app predicted my period to start on Jan 1... my period is pretty regular and usually starts within a day of the predicted start date... however I went in to plot my period is late today and the app pushed my start date for my period til Jan 4... confused??? I took a PT on 12/28/16 and got a negative... test yesterday and got a negative... had a pink like discharge this morning and thought my period was about to start... since then no more blood... trying to figure out when to test again! In hopes for a BFP!!!! Any idea ladies??? Happy New Year!!!