How do opk's work?

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I've not brought any yet, just wondering really as TTC no 2. Have stopped BF/expressing during the day and just feed at bedtime/through the night (2/3 times) to try and get ovulating again.
Do you just pee on the opk every day until it tells you the readings are high enough to be ovulating?
Jut don't want to waste money if there's no point yet...

When your body is trying to ovulate it releases lutenising hormone (LH) , which generally peaks about 24—48 hours before an egg is released. The opk measures LH levels and so is helpful in predicting when an egg is likely to be released. However, the peak can occur without an egg being released so the test doesn't tell you whether or not you actually ovulated. The only test that confirms ovulation is a day 21 progesterone blood test.

Yes you use them everyday and then once you get a positive, ovulation should occur 24-48 hours later. You can buy them cheaply online - I got a pack of 50 for under a tenner on Amazon. I will say - I had to stop breastfeeding totally before I conceived. Even though periods had returned, it took my first full cycle of no bf-ing before I conceived number 2. But fingers crossed you have more luck!