Seeing a doctor when you can't get pregnant?

Anyone care to share their story? I'm curious what to expect. I've made an appointment at my regular OBGYN because we've been TTC for 2 years. We have a 3 yr old already, so we're completely at a loss for why we're having so much trouble.

What tests are ordered? What's the first step? I've heard a lot about clomid? Is this something they'll prescribe if certain conditions are diagnosed or just a catch-all "try and see" medication that is used to help?