Thyroid meds causing fluid buildup/bag under eyes. what to do?

not likely: You don't say what kind of thyroid med you are taking. Thyroid hormone taken for underactive thyroid will not cause swelling around the eyes, but hypothyroidism can. Medications to lower overactive thyroids (methimazole, ptu) also are unlikely to cause eye swelling, but graves disease (the most common cause for hyperthyroidism) can affect the eyes.