Can whole body itching (without a rash) be caused by hashimoto's/adrenal insufficiency? and would this indicate under-treatment?

Depends: When you thyroid is underactive, your metabolism is operating at an abnormally slow rate. Your skin is unable to grow and replace itself as it should. Additionally, your sweat and oil-producing glands are unable to function as efficiently as they could otherwise. Dry itchy skin is most often associated with hypothyroidism, but your lab values are better indicators of disease control.