period late but negative test?¿

So I take medication for my periods to be on time due to thickening of my uterine lining.. ever since I started them my periods have not been even a single day late for months.. well my period is late (2 days) and I have no symptoms besides sore boobs.. is this normal? I took a pregnancy test tonight and it was negative. Should I take another one or assume AF is just late?