Who should I talk to about my sleep disorder?

Sleep disorders. Sleep disorders can usually be best assessed and treated by a Psychologist or Physician expert in sleep disorders. Insomnia for example is usually best treated with Cognitive Behavioral Treatment for Insomnia. This tends to be a specialty that is usually treated by a Psychologist. More info from this provider.
Your PCP. Your primary care doctor can perform a thorough assessment of your sleeping issues. Also, try to improve your sleep hygiene or "all behavioral and environmental factors that precede sleep and may interfere with sleep.".