Is this normal?

Okay so I always have had irregular periods but I’ve never exactly kept up with them until I downloaded this app the last time I was on my period. I logged my period on here the last time I was on it and as soon as it ended. According to this app I am 13 days late and I am sexually active. My doctor told me my cycle could be changing bc of my schedule change with school and work. Should I be worried? I’m scared that I’m pregnant.