i started my periods very young, i think i was 9, and mine were like that for a while, id have ot so i was on for like 2 weeks then wouldn't be on the next, then back to normal then really heavy, the doctor ended up putting me on the pill to see if that would help, it kind of did buit ended up getting other symptoms.
i've just been given those tablets now as my periods have started to get heavy again, but have found they don't make any difference.
i suggest you should go to your doctor and ask them to prescribe something else.
good luck x
just wait it out and see, if its longer than a week go see them, its normal for your period to be iregular sometimes. good luck