You're 13 like me. Is this your first period or have you been having them for a few years. If you have only had them for your first time like 5 months ago, they're bound to be irregular and don't worry at your age it's perfectly normal. If you start to notice really unusual changes maybe go to see a doctor, but I think everything is very normal at the moment. And stressing about it can actually make it late.
Well at 13 it's perfectly normal to have irregular periods so I'd say to hold off a bit cause they will probably stabilise over time and birth control can really mess up your bodies natural functions so is say wait until you're sexually active or you're ready for sex to go on the pill xx