All women should see a gynecologist if (1) they want to change their current method of birth control or (2) they are thinking about having sex for the first time. Anyone over the age of 16 should be visiting the gynecologist yearly for her regular gyno exam and pap smear anyway. You should try to visit the same doctor/nurse practitioner every time you go; this way, you will feel comfortable asking her questions about sex and birth control, and she will know your medical history, which will help her better prescribe and monitor your birth control methods.
Make sure you read up on the birth control method you are considering before you visit the doctor. You'll be more prepared to go over your questions/concerns with your gynecologist. You can also pick up pamphlets on various methods from your local clinic or doctor's office before you go in for your appointment.
If you're concerned about losing your sex drive, ask your doctor about it. Your gynecologist needs to know all of your needs so she can help you pick the right method of birth control.