Confusing + ovulation tests... can herbs affect it???

I am using two different kinds of tests to try and detect ovulation (my cycles have been very irregular)... ovulation test strips and a Clearblue Easy Fertility Monitor. The CBE monitor is used, so I can't be sure that it is fully functional yet as I have not used it long enough to have a positive ovulation result (another reason for me to use ovulation predictor strips in addition to the CBE monitor).

My cycles have been fairly long lately, but I have been using vitex/chasteberry in order to shorten them and restore overall balance to my hormones. As a result, they have gone from being 40+ days to being 40 days, then 36 days, and now who knows... maybe this one will be even shorter.

Here's the issue... today is cycle day 13 and I got a positive result on my ovulation test strip, but my CBE monitor still shows 'low fertility'. I don't know which to believe!! It's a little early for a positive, but if my cycle is in fact getting shorter, it would make sense.

Can vitex/chasteberry or false unicorn root cause a false positive on an ovulation prediction strip? Should I assume that the ovulation test is correct and that the CBE monitor may just be off?? Should I re-test later on today? I'm confused and not sure what to think... any input would be appreciated!
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