pjeaamrels

Hi everyone
I'm getting worried, i'm currently 17 years old and for the past five months or so i've been bleeding every two weeks when i used to just get my period once every 30 days as normal. However, recently its one week i have my actual period -heavy and lasting for 4-6 days, and then after two weeks is dark brown spotting for 3-5 days.. I looked into this at the time and figured it just be mid-cycle bleeding. However, now i've got my full on period, when my last one was two weeks ago!! I did take the morning after pill about three weeks ago so it could be that, plus the fact i've been more stressed out lately, and have also joined the gym.. However, i'm still worried Has anyone been experiencing something similar?
Thanks so much