Why would your thyroid become enlarged if your already on levothyroxine and medicine has been properly adjusted. ?

Several reasons: The thyroid can enlarge due to incorrect replacement, inflammation or from nodule formation. See a qualified endocrinologist.

We talk of ...: Thyroid function and structure separately- sometimes related, sometimes not so if function now ok with med , must address structure issues, ? Nodules, tumor, thyroiditis see endocrinologists.