Do you have a glucometer to check your blood sugar level? That would tell you if you are not handling carbs effectively, because your blood glucose would be high after a high carb meal and it would stay high. The way to check would be to measure your blood glucose before eating and then again exactly 2 hours after eating.
Hypothyroidism can affect blood sugar levels, so the two things could well be linked. Hopefully the endocrinologist will sort things out for you.