OPK's reliable?

This is my first cycle using an OPK and I am on day 11 of my cycle.  Since my  cycles for the past 5 months have fluctuated from 23-29 days, I started to test on day 6. I'm now on day 12 and I'm hoping for an LH surge. Should I be concerned? I had EWCM on Tuesday so I was sure that I was ov soon but nothing yet! My dr told me to schedule a visit after 6 months of TTC and this is my 6th month.