Hello @arabon
Only speaking from my most recent battle with diabetes. I was diagnosed couple months ago, June 24th of this year.

Most physicians do not run to diagnose a tumor. Usually they tread lightly ruling out more common causes. So it would make more sense to start at the beginning.

Since normal thyroid function is essential to regulate energy metabolism, abnormal thyroid function may have profound effects on blood glucose control in diabetes. Both hyperthyroidism and hypothyroidism can affect the course of diabetes, but their effects are somewhat different. Hyperthyroidism is typically associated with worsening blood glucose control and increased insulin requirements. The excessive thyroid hormone causes increased glucose production in the liver, rapid absorption of glucose through the intestines, and increased insulin resistance (a condition in which the body does not use insulin efficiently). It may be important to consider underlying thyroid disorder if a person has unexplained weight loss, deterioration in blood glucose control, or increased insulin requirements. Sometimes hyperthyroidism may even unmask latent diabetes.

It would be reasonable for your physician to have you monitor your diet & blood glucose levels. Have they checked your glycated hemoglobin other wise known as hemoglobin A1C or HbA1c? Here is a link to help understand this test and it’s importance...
https://www.mayoclinic.org/tests-procedures/a1c-test/about/pac-20384643
Are you monitoring your blood glucose and your tracking your daily dietary intake?

Thanks
Dawn