What could cause my high blood pressure?

im 17 years old and im not over weight (im bout 100 lbs). i had swine flu not to long ago and when i was at the doctors they said i had high blood pressure. my mom, being a nurse, said that the normal blood pressure is between 60 and 80 and showed me how to take it myself. since then ive been checking my blood pressure and im still around 100 and 106 (even without doing any activity). ive never had any problems with my heart before or know of any in my family (that ive heard of at least). dose anyone know what might be causing this?