TSH is not the best indicator of thyroid hormone function, it can be used to indicate a problem if it is very high or low, but freeT4 and freeT3 are the actual thyroid hormones and are more important in determining thyroid function. The thyroid makes mostly T4 hormone, which is then converted to the active hormone T3 which is used throughout the body. Hypothyroidism is caused low T3 activity in the tissues. Most people feel best and have fewer hypothyroidism symptoms when freeT4 is in the top 50% of the range, and when freeT3 is in the top 1/3 of the range. I'm not sure if your T3 is freeT3, but your freeT4 is in the lower part of the range (about 19%), so I wouldn't be surprised if you were experiencing hypothyroidism symptoms with FT4 at that level.
Have you been tested for Hashimoto's? Hashimoto's is an autoimmune disease where your body develops antibodies against your thyroid. As your immune system attacks the thyroid, this can cause a decrease in the thyroid hormones produced, stimulating thyroid growth by increases in TSH as well as hypothyroidism symptoms. With an increase in TSH, the thyroid can grow and produce more thyroid hormone (T4), causing TSH to go back down (and can cause hyperthyroidism symptoms for some people). Many people with Hashimoto's have hypo symptoms but TSH in the normal range because of this fluctuation. Eventually, if your thyroid continues to be attacked by your immune system, you may need to take supplemental thyroid hormone medication. TSH can be in the normal range or even low when you have Hashimoto's because of this fluctuation. The test for Hashimoto's is an antibody test for thyroid peroxidase (TPO) and thyroglobulin (Tg). Many people with hypothyroidism in countries where iodine is added to salt have hypothyroidism due to Hashimoto's.
I bring up Hashimoto's because it can cause goiter, and with your TSH in the normal (or low) range it is probably something that should be tested. It doesn't mean you have Hashimoto's, but it is something that should be checked based on your goiter, your thyroid hormones, and your hypothyroidism symptoms. If you do have Hashimoto's, some people can slow down the progression of the disease by modifying their diets, some people take thyroid hormone (natural or synthetic) to prevent thyroid growth and get their thyroid hormone up to normal levels.
TSI is thyroid stimulating immunoglobulin and is found in people with Graves disease, another autoimmune disease that targets the thyroid and causes hyperthyroidism. TSI in normal range indicates you probably don't have Graves. Both Graves disease and Hashimoto's can cause goiters. I'm hoping your endocrinologist is willing to test for Hashimoto's because hypo symptoms and low T3 and T4 point more towards Hashi's than Graves disease, but sometimes doctors like to treat just by looking at TSH which is not helpful and can be very frustrating for people with thyroid problems.
I hope this helps explain what might be going on, and good luck with your ultrasound!
In addition to the good info provided by Sarahjogs, there is central hypothyroidism, caused by hypothalamus/pituitary dysfunction, characterized by TSH levels that result in inadequate stimulation of the thyroid gland and thus inadequate thyroid hormone levels. Your Free T4 is low in a range that is too broad and skewed to the low end, and thus low levels are suspect. Your Total T3 is also below mid-range, but you really need to know the biologically active form, which is Free T3. Even more important for diagnosis of potential hypothyroidism, the best indicator is an evaluation for symptoms that occur more frequently with hypothyroidism. So please tell us about the specific symptoms you have.
Note also that hypothyroidism is not just inadequate thyroid hormone, but instead is best defined as insufficient T3 effect in tissue throughout the body due to inadequate supply of, or response to, thyroid hormone. Your thyroid status is the clinical state resulting from the level of TISSUE T3 EFFECT in your body. So both the supply and the response to thyroid hormone ares important. The response is affected by a number of variables, including cortisol, Vitamin D, B12 and ferritin.
At first opportunity you should ask to be tested for both Free T4 and Free T3, cortisol, Vitamin D, B12 and ferritin. Vitamin D should be at least 50 ng/mL, B12 in the upper part of its range, and ferritin should be t least 100. You should also find out if your doctor is going to be willing to treat you clinically, based on symptoms, rather than based on lab tests. Also ask if the doctor is willing to prescribe T3 med such as NatureThroid, Armour Thyroid and Ccytomel if needed to optimize your Free T3 level and relieve hypo symptoms. If either answer is no, then you will need to find a good thyroid doctor that will do so. If you think you might need help locating a good thyroid doctor we may be able to recommend one if you give us your location.
If you want to confirm anything I have said, please click on my name and then scroll down to my Journal and read at least the one page Overview of a paper on Diagnosis and Treatment of Hypothyroidism: A Patient's Perspective.
Thank you for your response.. I will ask for the test suggested. I wonder in a goiter pressing on the thyroid could make the levels low and when the goiter is taken care of the thyroid will be able to work properly? My symptoms are fatigue,cold,brain fog, aniexty/depression, no motivation)
No, I don't think the goiter is affecting the thyroid gland like you stated. Taken together those symptoms, supported by your test results, are indicative of hypothyroidism, and the need for thyroid medication. .