If you were calling someone from the dermatologist’s office, you would probably just say “I’m at the dermatologist “ or “I’m at the dermatologist’s” (in most cases “clinic” or “office” doesn’t add any useful info, and would be skipped.) I think it’s more common to say “I’m going to a dermatologist” to describe that you are under the care of a dermatologist. (“Seeing” doesn’t necessarily mean dating but it’s used for more personal type professions like therapist or psychiatrist, where ‘going to’ also works well)

As regards your second sentence, "I'm seeing a dermatologist " could mean either that you were seeing a dermatologist for treatment of a skin condition or that you were dating a dermatologist, however there is no real risk of confusion because it would be clear from the context what you meant. Unless it was clear from the context that you were talking about dating, most people would understand that you were seeing a dermatologist professionally.

@Robert Thank you!

Hello, Seul! Great questions. It would sound more natural to say, "I'm at a dermatology clinic (not dermatological)". If you were waiting in a dermatology clinic and said, "I'm seeing a dermatologist", it would be understood that you were seeking medical treatment and not dating a dermatologist. You could also say the following: "I'm at the dermatologist's office." "I'm waiting to see a dermatologist." "I have an appointment to see the dermatologist." All of these examples could be used interchangeably and would be perfectly understood. I hope these suggestions help. If you would like to increase your fluency with professional English lessons, I am a teacher on Italki. I am currently accepting new students and would be happy to help!

“I’m seeing a dermatologist for my skin condition, (such as acne. psoriasis, moles, etc). Or I am being seen by a dermatologist.