TTC for 3 months- positive peak OPK once

Katherine
TTC since December 2016 in which it was the only month I had two peak fertility days on the OPK. Haven't gotten peak fertility since. I was tested in 10/2015 for PCOS but all tests can back negative and ultrasound showed plenty of healthy normal looking eggs.  
Is it possible to take OPK test wrong? I've had high days for 13-14 days on average.