So I need some help on this! Please!

So last month and the month before I have been starting my period on the 17th or 18th every month now. Well since it was leap day 2 week ago I'm confused on why I haven't started my period the 17th. I know I sound dumb but I'm really confused. When the 17th came and I didn't start the app moved my period to start tomorrow. So am I late or no. I took a test and its negative.