im 17 years old. i got my period when i was 12 years old, and it was a little irregular for a bit but then it returned to a regular schedule until i was 14-15. then from oct. 2005 until about jan. 2007 i didnt get my period and my doctor said that was normal.(?) so then i got my period from jan 2007 until oct 2007 reguluary, then it just stopped and i havent got it since then. what could be the problem?