When to use OPK, OPK questions!

Hello all,

When should I start using my opk? I’m on day 4 of my period and obviously know atleast wait until I’m done bleeding. Last month I tested every day and when I finally got my positive I BD the day of and the day after. Well. AF showed up right on time. I have PCOS and missed a period a few months ago but it was due to having high TSH and super low vitamin D. My doctor prescribed me metformin, vitamin D 3000, told me use vitex, eat right, walk, drink more water and see what happens. Well I started using my opks last month and I’m really confused about the whole thing. I also got a bbt. I haven’t been consistent with using it because I forget but this month I’m going hardcore because I got my little heart broken last cycle and I’m ready to try hard. Someone help! I have miscarried 3 times and none of which were planned. This last one made us really want a baby. So here I am.