Confused ?

I was supposed to start my period this month on the 10 of April I had my last period on the 13 of March my cycle last about 6-7 days but it hasn’t gotten here yet. I haven’t had any sex or any sort of intercourse and I also remember going to the doctor this month to ask about birthcontrol and that was not so long ago. He made me take a pregnancy test which was negative. What could be the reason as to why my period hasn’t started. This was an issue too last month my period was not starting on the day my <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">period tracker</a> was saying and it had me super worried. I suspected bc of the extra days in the month but I never looked into it