You have a swelling or inflammation of the thyroid. In some cases thyroiditis is self induced with something that has reacted in the body causing it... example - medications or diet or over stress ( body and/or mind) to name a few.
In some cases thyroiditis can be reverse and in some its not.
Did you have labs supporting this ultra sound? Getting the autoimmune and thyroid labs would be a great indictor on what really is happening and comparing those results to the US scan.