All negative :(

I've been using clearblue opk for the past four months and I have never once gotten a positive. My gf took one and on her second day of testing got a smiley face and she has pcos. My cycles are irregular but even after using all 20 tests for just a single cylce, I can never get a positive. Sometimes I get an error but I'm not sure what that means. Does anybody know what I'm doing wrong or have any advice? This is our 5th month using the opk and has caused us to miss out on TTC since we are a lesbian couple doing AI. HELP??!!??