Go to primary doc
The first line test to assess thyroid fxn is your TSH level, which is done with a blood draw sent to lab.
Based on this and correlating it with clinical symptoms, medical hx, and fam hx, you may need further follow up with an endocrinologist which usually is an md, but can be a do with further fellowship training. But start with your primary doctor. She/he can help you sort out your problem.