My ex has thyroid problems and has only been diagnosed with depression. But I know from living with him that I could chart his moods by the seasons, and his episodes of agitation are not exactly manic, and are short lived, but are extremely impulsive and destructive.
I think there is a type of bi polar disorder which is characterized by rapid cycling, or by mild escalation coupled with long periods of depression.
Even when we were married, he did not give his psychiatrist permission to discuss his diagnosis with me.
I think seeing an endocrinologist is a good idea, or having your family practitioner refer you to a specialist who can check out the thyroid. A good psychiatrist will also check out the connection, and work to have the best possible combination of medications.
A good place to learn about bipolar disorder and diagnosis is
www.bipolarworld.net.