Period every two weeks?

Im 16 and for two years i've had my period every two weeks but for the first week i would get it for 7 days then the second would only last for 4 days?(they are very light) A year ago i went to the dr and got tested to see if i was anemic. Fortunately they said I wasn't anemic. But it has yet to regulate im going to the dr.'s on monday to DEMAND for a gyno to get it regulated. I just want to know if it's normal and has anybody had this problem? I'm afraid that even though my tests said negative, I might end up to become anemic and I wouldn't know what to do if i found out i was.