Good afternoon lovely ladies!

I'm starting OPK's this month which I've never used before. I was looking at purchasing a bulk amount online however I also purchased some more Elevit today from the pharmacy and decided to purchase some ovulation tests (Forelife which the pharmacist said is one of the best brands that don't break your bank account). Anyway it was only a box of 7 tests and I don't want to waste them so need your advice on when I should start using the tests?

The information leaflet included in the box says that my cycle length being 37 and 38 days then I should start testing on either CD 21 or 22 however since last night I have noticed that I'm starting to get an increasing show of CM when I wipe (sorry if TMI). Do you think this is just my body getting ready for O or would you start testing right away just to be sure? I've never really paid attention to what days of the month my CM increases before and this is the first time I've actually started marking it on the calender.

Any suggestions would be great