Have you been tested for Graves Disease and/or Hashimoto's Thyroiditis? Both of these are autoimmune conditions that present with hyperthyroidism (low TSH and Free T4 and Free T3 in the upper ranges - that's assuming you had the FREE T4 and FREE T3 tested vs Total T4 and Total T3...
It's not just carbimazole that can cause swelling of the thyroid or nodular enlargement. So can thyroid conditions, in general. Hyperthyroidism can end up causing thyroid storm, which is a life-threatening condition if it's not treated.
Are you, currently, having problems with your windpipe being compromised or is this just a fear you have?