How can u tell UR ovulating and does an abortion affects u getting pregnant again

I can't tell when I'm ovulating and I have a regular period every 30 day and I been with my hubby for a year he cums in me but we still didn't get pregnant cuz I can't tell wenI'm ovulating   getting pissed like I came on my period sept 22 2014 and I have it for 6 days staring on the 22 and came off on the 27 wen am I fertile can anyone help me plz tips will help thx