You are still very young. The periods or the menstrual cycles take sometime to settle. The time period can vary in different women/girls. The periods become settled once the cycles become ovulatory (i.e, with egg release happening every month). In and anovulatory cycle these problems can persist.
You can expect to get your periods regularised and also the bleeding to become normal once you start getting 'ovulatory' cycles.
Hope this helps.