I'm sorry to hear about your dog passing away and the was hypothyroid just like you. Did you give him thyroid medication? This endocrinologist sounds more like one who focuses on diabetes and is not familiar with thyroid. Fasting from food isn't done for testing TSH or TPO. Did he test your free thyroid hormones FT3 and FT4, or is he just going by TSH? TSH is not a reliable test for your thyroid because it's not a thyroid hormone.
The only fasting that is done before testing is fasting from thyroid medication the morning of your tests. What were your results from the TG antibody test, or did the doctor not remember that there are two? TSH isn't a thyroid hormone. It's from pituitary but it communicates with your thyroid and tells it how much thyroid hormone to produce. TSH 3.87 is too high, is hypo. You don't want it to be left that high. Your pituitary is telling your thyroid to try to make more thyroid hormones, T4 and T3. Your symptoms of weight gain, constipation, sleep problems, low physical activity are hypo signs. I'm sorry to say that your TSH will not resolve on it's own. It sounds like you've been hypo for over 5 years with constipation and other symptoms. You need a doctor to run a complete thyroid panel on you so that your thyroid can be correctly evaluated, which is impossible by TSH and one antibody. Do you also have diabetes? Diabetes can be related to being hypothyroid. I hope he tested your A1C, fasting glucose and insulin. Since he didn't test your thyroid (TSH is pituitary) this makes me concerned about his ability as an endocrinologist to diagnose health conditions.
First thing to understand is that the correct definition for hypothyroidism is not just inadequate thyroid hormone. Instead it is "insufficient T3 effect in tissue throughout the body due to inadequate supply of, or response to, thyroid hormone." It is the TISSUE T3 EFFECT that determines your thyroid status. TSH is a pituitary hormone that is affected by so many things that it has only a weak correlation with the biologically active thyroid hormones, Free T4 and Free T3, and a negligible correlation with TISSUE T3 EFFECT. Thus TSH is useful as an indicator of thyroid status only when it is at extreme values. Your TSH does not come anywhere near such a level.
The best way to assess a person's thyroid status is an integrated approach including a full family history, evaluation for symptoms that occur more frequently with hypothyroidism, and finally extended biochemical testing. Tests should include Free T4 and Free T3 (not Total T4 and Total T3) every time you go in for tests. A TSH test with followup to TPO ab and TG ab, if TSH is high. Reverse T3 is also useful, along with cortisol. Since hypo patients are so frequently deficient in Vitamin D, B12 and ferritin, those should be tested and then supplemented to optimize. D should be at least 50 ng/mL, B12 n the upper end of its range, and ferritin should be at least 100.
You have mentioned several symptoms that frequently occur with hypothyroidism. So I suggest that you try to get the additional testing done as the next step. Then post results and reference ranges here and we will be glad to help interpret and advise further.
Also keep in mind that a good thyroid doctor will diagnose and treat a hypothyroid patient clinically, by adjusting Free T4 and Free T3 levels as needed to relieve symptoms, rather than based on biochemical tests, especially TSH. As mentioned TSH is useful for diagnosis only when at extreme levels. TSH is useful in distinguishing between primary central hypothyroidism.
If you want to confirm anything I have said, click on my name and then scroll down to my Journal and read at least the one page overview of a full paper on Diagnosis and Treatment of Hypothyroidism: a Patient's Perspective.
Some doctors consider a TSH of 3.87 hypo enough to go on medication if you have symptoms and have tested positive for Hashimoto's or Graves. Has your doctor checked your Thyroglobulin (Tg) levels? Tg is basically another antibody that has been associated with Hashimoto's. Have they checked your FT3 and FT4 levels?
My lab reference range for TSH is a max of 3.5 mU/L.
My lab reference range for TSH is a max of 3.5 mU/L. I gained weight from hypo when my TSH was in the mid 3's.
You should mention to your doctor that central hypothyroidism does not manifest a high TSH, and that central hypothyroidism is not a rarity, just that it is rarely diagnosed due to inordinate attention to TSH only. You can also tell him that TSH has only a weak correlation with the biologically active thyroid hormones, Free T4 and Free T3 and it has a negligible correlation with Tissue T3 Effect, which determines a person's thyroid status. So TSH is useful as a diagnostic only when it is at extreme levels. An evaluation for symptoms that occur more frequently with hypothyroidism is the most important consideration in diagnosing a person. Next is testing for Free T4 and Free T3. Also as mentioned it is important to initially test for Reverse T3 and cortisol. Also due to their effect on the response to thyroid hormone, Vitamin D, B12 and ferritin should be tested and supplemented as needed to optimize. D should be at least 50 ng/mL, B12 in the upper part of its range, and ferritin should be at least 100.
You can find all this info in the paper linked in my Journal.
As I mentioned previously TSH is totally inadequate for diagnosis of thyroid issues unless it is at extreme levels, either high or low. Otherwise the most important indicators of your thyroid status are symptoms that occur more frequently with hypothyroidism and then biochemical tests, mainly for Free T4 and Free T3 (not the same as Total T4 and Total T3). Also as mentioned, it is important to initially test for Reverse T3 and cortisol. Also, due to their effect on the response to thyroid hormone, Vitamin D, B12 and ferritin should be tested and supplemented as needed to optimize. D should be at least 50 ng/mL, B12 in the upper part of its range, and ferritin should be at least 100.
If you cannot get your doctor to even consider the possibility of central hypothyroidism and do these tests, then you are wasting your time there and need to find a good thyroid doctor, instead of waiting around for months with the likelihood of the same response.