OPK testing

Hi all, looking for some help with opk testing. How many times a day do you test and when? I've been testing since Sunday last week around 6pm but didn't test on Sat this weekend just gone and think that may have been when ovulated as tests were getting stronger but then test yesterday and this morn (first time testing in the morn) is light. the trouble im finding is that I go to the loo a lot and often drink 3 litres ish a day. have cut down on drinking and tried to hold urine for 4 hours before testing in the eve but easier said than done. strangely have been cramping a lot last few days. Thanks in advance for any info!