When to see a doctor when TTC

Staci
My husband and I have been trying (not super hard to be honest, haven't been testing using Opks) for over a year and a half. I'm getting so discouraged and frustrated. :-( Not once have we had even a glimmer of a possible positive pregnancy test
​Should I be concerned and going to see my doctor? I've been taking a prenatal since we decided to start trying and aren't using any lubricants (we've  heard some can be bad for the sperm)
​Thoughts??