I'm 23 yrs old, I didn't get my period until I was a freshman in high school, I was 16 so I guess that is somewhat normal, though I was later than all my friends. After my first period ever I didn't have a period for months at least 5. I went to the doctor she gave me a pregnancy test even though I wasn't sexually active. When I got my next period I would have them every other month. At age 20 I. Went three months without a period I wasn't having sex so I know I wasn't pregnant. Now I'm 23 and sexually active I had my last period sept 2011. I took a pregnancy test and it was negative. Its been 5 months and this can't be normal. Any ideas as to what can be wrong??