Most, but not all thyroid disorders stem from disease.
There are several that fall into the 'most common' category.
It's very important to determine the cause for your thyroid disorder, be it hyper or hypo. It will make a difference in how you treat it with meds, diet and life style.
Never settle for a doc that tells "you all is fine, your labs are 'within normal range'" if you know that there is something wrong with you. Be assertive and stand your ground, you are fighting - not only for your quality of life, but in some cases for your very life.
Isn't you life worth finding out what's wrong?