How do I get pregnant with a irregular period ?

Andrea
I have a 6 year old daughter, I also had a MC in March of this year, we have been ttc since then , however I normal have a 28 day cycle but the last 3 months my cycle have become irregular - at times 3 weeks late other times 3 day early. I don't want to get addicted to opk- any positive advice on best time to get pregnant with a irregular