Late periods?

I'm 17, sexually active (to get that out of the way)

In April is when I started to get periods late.. And its still happening.. Sometimes I'm 3 days late , sometimes I'm a week late.. I've had ovarian cyst before n ik that could be the reason but they popped in may , near the end.. I don't understand why I can never be on time .. Is something wrong with my body? Is this normal?