No positive opk's.

So we have been ttc for about 9 months now with no luck. Both of us are in our mid 20's. This month I decided to start ovulation testing. Well I am on CD19 and still no positives. I have regular periods every month around the same time so I never thought I wouldn't be ovulating. Should I be concerned? I figured I would keep testing for another month or two before bringing it up to my doctor. Just wondering if y'all had any advice or similar situations. Thanks in advance :)