I've been trying to calculate when i'm ovulating but the past two months my period has come early. how can i tell when i'm ovulating & why am i early?

14 days before: An easy way to remember ovulation is that it occurs 14 days before your next cycle. If you know how many days between periods then you can calculate an approximate ovulation date. If your cycles are irregular than predicting ovulation is almost impossible. At age 19 i suspect you're trying to avoid pregnancy. Why not just start birth-control for cycle regulation?

Ovulation: Easiest solution is to buy the ovulation kits, but see your gyn if irregularities persist.