Primary care. Patients can start with there primary care doctor, who can screen for sleep apnea and order a sleep test. The test itself is read usually by a sleep specialist. Sleep specialists can be found in many specialties. Often they are pulmonologists (lung doctors) because the therapy involves a machine that affects the air pressure in the airway. Still neurologists, and ENT doctors often have an interest.
Gather Information. A primary care can do a physical evaluation as well as gather clinical symptoms to evaluate you for sleep apnea. An epworth sleepiness scale and berlin questionnaire can be answered that can help gauge the degree of sleepiness or risk for having sleep apnea. A sleep study will ultimately need to be done to get a formal diagnosis.
Primary Care MD. Start with your primary care doc. He/she will direct evaluation based on his/her evaluation.