When dealing with any aspect of mental health services, make sure you're prepared before the initial consultation. If you have any prior consultation or treatment reports, medical records, prescription information and the like, be sure to organize this data and have it with you.
Few mental health service professionals are going to be upset if you seek a second opinion. Your health, mental and otherwise, is too important to hinge on the testimony of one doctor, no matter how good. Your doctor might even be willing to offer you a referral for the second opinion.