It could be that you aren't on sufficient thyroid hormones as T3 is needed particularly by heart and brain as well as our billions of receptor cells. T4 - levothyroxine - is inactive and has to convert to T3.
Maybe you aren't converting levo (T4) or aren't on a sufficient dose to provide a Free T3 towards the upper part of the range.
Quarterly B12 injections aren't always sufficient and many supplement with sublingual B12 methylcobalamin tablets.
Ask your doctor if you can have a heart check - just to eliminate problems.
Is your blood test next week for the earliest possible time, fasting (you can drink water)? and allow a gap of 24 hours between your last dose of levo and the test? If not change your appointment. Ask GP for TSH, T4, T3, Free T4, Free T3, B12, Vit D, iron, ferritin and folate. (some labs wont and I think most GPs are happy with a TSH/T4 only but it doesn't give a whole picture of our thyroid hormone health.
Get a print-out with the ranges and put on a new post for comments.
We have to take our own health into our own hands as it appears that the medical profession are so poorly trained in assisting patients with dysfunctions of the thyroid gland.