PLEASE HELP!!

I have used this app awhile back to track my periods, however I delete it a couple weeks ago due to being lazy at putting my results in and so on. HOWEVER, I started my period on January 21, February on the 18, and in March I started my period on the 19....... This month, I have yet to get mine.... Should I be worried?? THIS APP SAYS I SHOULD HAVE gotten my period this month the 16.... Please help ladies!!