Starting OPK’s- help lol

My husband & I have been trying for months... so two months I started using ovulation prediction kits. I never had my LH surge, so I wasn’t sure if I was using them correctly. Turns out I have PCOS, and wasn’t ovulating at all... so with that being said, she started me on Metformin. 2000mg’s a day. This is the start of my third week taking it. For the first time, my period came when it was expected, on CD 22. So now I know that my periods are regulating, which hopefully means I’ll start ovulating.

What day do you recommend for me to start using opk’s again? I wanna make sure I do it right.