OPK help

Helen • Happy family with 8 year old 6 year old and 4 year old 🙂
I've recently been taking pregnancy tests and they all came back negative, so I decided to go to the docs and he confirmed that I wasn't pregnant, so I've decided to buy some ovulation tests as I'm currently day 7 late but I think I'm irregular, shall I start using them straight away or wait till my next period? Any help please