if you go to the doctor at any age, your parents don't and won't know unless you tell them yourself. The only exception is if someone's life (doesn't have to be yours) is a risk from what you told the doctors, at that point they would have to inform your legal guardian/ parent.
As you are over 18, I don't think anyone gets told anything, even if there is life at risk as once you are 18 you are an adult (or thats what it is for UK - assuming you are in UK)