My OPKs seem to be behaving a bit weird- no test line at all on multiple days when I usually get a faint one, control line very faint, taking ages for the wee to travel across them, etc. I noticed on the packs it says to store below 30 degrees, and it's possible they got hotter than that in the heatwave as I didn't really store them responsibly- inside washbag on the windowsill 
Has anyone else's stopped working? I also considered that I might be overhydrated but have tried not drinking much for a few hours and still had issues.