I have a large goiter with many symptoms of hypothyroidism yet my labs are always normal, why is this?

Needs treatment: A simple goiter can occur without a known reason. It can occur when the thyroid gland is not able to make enough thyroid hormone to meet the body's needs. This can be due to, for example, a lack of iodine in a person's diet. To make up for the shortage of thyroid hormone, the thyroid gland grows larger.

Your thyroid has: Enlarged in order to continue producing adequate amounts of thyroid hormone, much like a muscle grows with prolonged exercise. You can halt this enlargement and often even cause some shrinkage by beginning an appropriate dose of brand name T4 replacement. Check w/your doctor, it's one of the indication for treatment.