Endocrinologist. the internist will be able to evaluate your thyroid, however, if abnormalities are found upon testing, he/she will likely refer you to an endocrinologist for further evaluation and management. .
A PCP can do it. As a general internist, i treat people with under active thyroid all the time. That requires occasional bloodwork and possible dose adjustments. If the patient has over active thyroid, i generally refer that to an endocrinologist for further evaluation and simply maintain patient on recommended meds. For thyroid nodules/masses, i often get a thyroid sonogram and base next steps on the findings.
Endocrinologist. Thyroid diseases are covered in the extra training of an endocrinologist making them more knowledgable in this area than an internist on average.