Irregular periods.

Okay so my period has always been irregular but it always last for 7 days. It could be in the beginning of the month or the middle or the end. In Feburary I think it was the 13th it started & last 7 days. I had sex on the last day of my period. (Never again lol there was a mess.) and then my period in March never came but in April it did and lasted my normal 7 days. I've had my period since age 12 or 13 I can't remember and I'm 16 now. Should I be concerned about that ?? Or is it just cause I'm irregular?