Readjust your insulin. Thyroid supplementation frequently raises BG. Thyroid needs to be taken every day, a needed hormone. TSH is high when T4 when is low, so taking less levothryroxine won't lower your BG & it's not TSH effecting your BG anyway. This is a wonderful site for thyroid info http://tiredthyroid.com/.
Levothyroxine is T4 only. T4 is converted to T3. Many do far better on natural dessicated thyroid (Armour, Nature Throid, Erfa, WP Thyroid) which contains T4 & T3 because it's common to have problems converting T4 to T3.