Operations on the thyroid are done by surgeons. medical, non-surgical treatment is handled by endocrinologists.
An oncologist treats people with cancer.
a gynecologist
Veterinarians treat animals including cats and dogs.
Cardiologist
Obstetrician
There isn't a type of doctor who specifically treats doctors.
A psychiatrist
ENT specialisd
An endocrinologist?
A doctor
A physician who specializes in treating the elderly is known as a geriatrician.
If you mean newborns, which I'm guessing you did, the physician responsible for that would be a neonatologist.