Enlarged thyroid. goiter?

my thyroid is enlarged. is this a goiter? i'm not sure what that is. you can barely see it in my neck, but can feel it. it has been "large" for awhile, around 6 years. the doctors always did TSH bloodwork. always came back normal, so they said it was fine since no lumps or pain associated with it. this year my doctor did a TSH test again, the results are not back yet. she also recommended i get an ultrasound. it is scheduled for next month. should i be worried. i am totally freaking out. i've read online it could be enlarged due to cancer. what else could this be? can your thyroid be enlarged for no reason? i am scared! all the other doctors acted like it was no big deal. i feel fine and no pain in the thyroid.

In addition to test for TSH your blood needs to be tested for T3 and T4 hormones as well.What was the last reading of TSH?
The article below may be helpful:
"Colloid goiter occurs occasionally as a diffuse enlargement of the thyroid gland in adolescent girls, and is especially frequent in this age group in endemic goiter areas. It occurs much less frequently in adults. Typically, the goiter is asymptomatic. The gland is usually symmetrically enlarged and feels soft or spongy.

The cause of the condition is unknown.
The small colloid goiter of adolescent girls may disappear over 1-3 years. On the other hand, it may grow gradually and evolve into the nontoxic multinodular goiter found in adults.
A diagnosis of colloid goiter cannot be made with certainty without histologic confirmation. Thyroid function tests are variable, but the results are frequently normal. Antithyroid antibodies are absent, if Hashimoto's thyroiditis is not present. Needle biopsy will confirm the diagnosis but is seldom warranted.

Reassurance that the lesion is not a malignant neoplasm, and that the thyroid is not overactive, is often the only therapy required. If the goiter is large, thyroid hormone may be given in an attempt to decrease its size. If one accepts the theory that the goiter has grown in response to a need for more thyroid hormone, it is logical to expect that exogenous thyroid hormone would cause it to decrease in size. Unfortunately, practice does not always bear out the theory. Only about 70% of patients will respond with complete or partial regression of goiter. If there are significant pressure symptoms or if the goiter is a serious cosmetic problem, administration of 131I or surgical resection may be indicated. Subsequent replacement therapy with T4 will be then necessary. "