Irregular periods when do you test?

Hi Ladies. I’ve always had regular periods between 28-30 days, and then I had a miscarriage in Dec. First 3 periods were regular after, then suddenly became irregular 38, 37, 30C. I’m just curious when you ladies with irregular periods start hpt testing? The negatives tests are heart breaking, curious to see what you use as a guide. I’m on C35, took a test on C29 (BFN). Had a positive opk on the 15th, but I also started taking vitex this month don’t know if it further is messing with my hormones.