Ttc...when to start ovulation testing?

N • 36 yrs old, Married to the love of my life! Trying for #3 since July 2015 after 2 losses!
Hi ladies! Question for the pros who know?? So I've been tracking my periods for the last 2 years. Finding out they are never on point! Usually within 2 to 3 days of each month. Which makes finding out the day of ovulation a challenge. Anyway, I thought I'd try the ovulation test trips and see where that leads. I know the more chances of intercourse after periods the better but that hasn't been working lol. So my question is if your periods are irregular and I just finished mine 3 days ago when would be a good time to start? I know there's a fertile window to. I took a test today just to test it out and there was the dark line with the faint line....not sure what that means. I've looked on the website www.surepredict.com to find out more. But I'm still confused as ever. Any guidance away from Google would be appreciated! Thanks ladies! Last shot before I go to the Dr for more intense testing! :)