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
A psychiatrist
ENT specialisd
There isn't a type of doctor who specifically treats doctors.
A doctor
An endocrinologist?
A Doctor Who treats children is called a paediatrician
If you mean newborns, which I'm guessing you did, the physician responsible for that would be a neonatologist.