A psychiatrist. Sometimes you will find family medicine doctors that may have been educated on psychotropic medications who may be comfortable prescribing, but OCD has so many unique features that I think it is important to deal directly with someone who specializes in psychiatry in order to accurately diagnose it as OCD, simply because it can mimic an anxiety disorder. Therefore a non-specialist can be confused about exactly what it is that a person has or that they're seeking help for or getting treatment for, or being prescribed medication for.
Once diagnoses, I would recommend counseling with a licensed clinical professional: a licensed professional counselor, a licensed psychologist, a licensed marriage and family therapist, a licensed social worker. It is important to have a conversation with the professional in advance to ensure that treating OCD is within their scope, that they have appropriate training beyond general counseling training because this is a disorder that, if it isn't treated aggressively, can be very disruptive and debilitating.
Every individual is different, and we certainly understand that OCD is a brain disorder like every other mental health disorder that we typically treat. As a clinical professional, I am always looking at and for life experiences, current or past, that have leave the individual feeling an overwhelming sense of powerlessness or being out of control. Almost always that is going to be rooted with or in some fear, that there have been experiences in the past or there are current experiences in which something leaves them feeling powerless or out of control - some threat. And what we do know is that if individuals (child, adolescent, or adult) has been exposed on an ongoing basis to stressful life events where there was some element of threat (they feared for their life, or they feared losing something important) that it can become traumatic for them and it can develop into ritual-like behaviors, which can be diagnosed as OCD. Also over time it can lead to a diagnosis of PTSD for women. You often see obsessive compulsive related symptoms with women who have PTSD because of fear and threat and powerlessness.