thinking of changing OB's

Hey ladies, I'm thinking of switching my ob mid pregnancy.. I absolutely love my doctor, but the office itself is what's making me want to switch! Yesterday I called concerning some cramping I had and the nurse said she would have the on call doctor or herself call me back that day... no call. This has happened before too when I was going to the hospital for severe nausea and dehydration, I called the office to speak to my doctor first about what he recommended I do or to even inform him that I was going, and again, the nurse said they'd call me back right away.. never got a call. I guess it's just frustrating to not be able to rely on your own doctor's office, like what else are they there for? How difficult is it to switch mid pregnancy? Thanks ladies