Do you ladies know?

Maybe this is the dumbest question but I've been sexually active for 8 months, and I barely started tracking my period for the past 3 months. I know that this app isn't as accurate but it says that I'm late by 3 days. Yesterday I thought i started because I bled a little but this morning I woke up and there's no blood or nothing. My pad is completely spotless. What could this be? Or is there a certain amount of days that could go as late?