Feeling discouraged

Ca

I’m starting to feel a little discouraged. I’ve been doing OPKs for a few months and I’ve never gotten a positive. AF is still coming but I’m having a hard time predicting when to BD. My husband works weird hours so we can’t always BD every other day. Could it be the brand of OPKs? Has this ever happened to anyone? My cycle is pretty irregular and can vary by a couple days to a couple weeks. Any help would be greatly appreciated.