Im 16 years old, and im really confused......

December 10th, 2012 i had a dark brown discharge on my pantyliner. I read this is older blood, so i was not worried. Then towards the end of July of this year, I was sitting on my bed and i felt something so i checked my pantyliner and there was blood! I was really happy i finally started my period. i mean 16 is really late...I went to the bathroom that night and (sorry if this is really graphic) i could see a little bit of flow in the toilet...but this time it was not red it was a dark brown color...

Days after this i still had to wear pads now and then from a semi heavy discharge of dark brown. Its so unpredictable i constantly have to wear a thick pad!! it goes through the panty liners...I put a tampon in because i was going swimming, and later as i was taking it out i saw blood on it with the brown discharge as well. So i figured i got my period again. Now today im having cramps and have been the past few days... i STILL have the brown discharge (have since december. it only stops for a few days at a time then comes again)I was camping and used a tampon, since i was swimming in a lake and obviously wasnt going to swim with a pad. I later took the tampon out and there was a little bit of blood on it...This has happened with the past 4 tampons i used this past few days. I arrived home and removed a tampon about 15 minutes ago and it had a good amount of blood on it but it wasnt soaked like it should be. So i sat on the toilet and waited for any flow.....nothing. I tried coughing and flexing my abs and just nothing will flow. Now im wearing a pad and waiting but nothing is coming out.