TSH is a useless test when taking thyroid med. Medication dosage should be whatever is needed to relieve hypo symptoms, not TSH levels that make the doctor happy. Our bodies are used to a continuous low flow of thyroid hormone (bothT4 and T3 ) from the thyroid gland, in the untreated state. When you take your med dosage all at once in a short time, it spikes thyroid levels for a short time and suppresses TSH for the day. This has been proved in several studies that I can link for you. But before that please tell us about which, if any, of the following symptoms you have.
Increased sensitivity to cold (temp. below 98.6 which is considered normal)
Constipation ( have to use fiber or laxatives)
Dry skin (have to use moisturizer)
Elevated blood cholesterol level
Muscle aches, tenderness and stiffness
Pain, stiffness or swelling in your joints
Heavier than normal or irregular menstrual periods
Slowed heart rate
Enlarged thyroid gland (goiter)
Also please post your thyroid related test results and their reference ranges shown on the lab report. If tested for Vitamin D, B12 and ferritin please post those also.
TSH is a pituitary hormone that is affected by so many things that it is useful as an indicator of thyroid status only when at extreme levels in the untreated state., indicating Hashimoto's Thyroiditis. When you start on thyroid med, as I explained above, TSH is basically a wasted test. Doctors don't understand what I explained about a suppressed TSH, however, so they want to decrease thyroid med when the TSH becomes too low for them to be comfortable. That is wrong. A good thyroid doctor will increase your thyeoid medication enough to relieve hypo symptoms, without increasing to the point of causing hyper symptoms. That sweet spot is called "clinical euthyroidism", which should be the whole objective of treatment, not biochemical euthyroidism, which means having TSH within range.
It is doubtful that your thyroid hormone levels were adequate even at 100 mcg of T4 med. After the reduction to 75 mcg, predictably you felt worse. Taking away one day of the 75 mcg meant a further reduction on average of almost 11 mcg per day, which would be worse yet for you. Your current lab results are inadequate. Your Free T4 is okay at mid-range, but if your Total T3, which is only 16% of its range, is indicative of your Free T3, then that is the main reason you are having those hypo symptoms and feeling so bad. There are recent scientific studies that have quantified for the first time the effect of Free T3 on symptoms. They found that symptom change is mainly related to Free T3 and less with Free T4, and hardly any with TSH.
You might find my similar experience interesting. I was hypo for around 40 years. It took me a long time to convince my doctor because my TSH was "within range". Finally I located this forum and learned about the importance of Free T3. Got my FT3 tested and confirmed as low in the range, due to poor conversion of the T4 in the 200 mcg of Synthroid I was on. Convinced that doctor to switch me to a desiccated type med containing both T4 and T3. After some tweaking of dosage that got my FT4 just below mid-range, and FT3 about 70% of its range, I felt better than I could ever remember. Of course everybody is different and may need different levels of FT4 and FT3. My point is the importance of Free T3 and that doctors usually don't even test for it and don't pay any attention to symptoms or FT3.
So you need to take info I can direct you to and give it to your doctor and ask to be treated clinically, as needed to relieve symptoms. If the doctor resists or refuses, then you will need to find a good thyroid doctor that will do so. If you will give us your location perhaps we can suggest a doctor in your general area who has been recommended by other thyroid patients. Also at first opportunity you need to get tested for both Free T3, Reverse t# (at least once) and cortisol and ferritin. Both your Vitamin D and B12 are lower than optimal. D should be at least 50 ng/ml, and B12 in the upper part of its range. So you need ot supplement for both of those to optimize. For info ferritin is a storage form or iron and it should be at least 100.
By the way I would not worry about the possibility of Erythromelalgia at this point. Get the other issues corrected and then you can reassess.
You are not being well served by your doctor for your thyroid problems. Your best bet would be to find a new doctor. If that is impossible for you, then try asking your doctor to refer you to an endocrinologist and hope that the endo is better than the doctor. The reason to ask for a referral is that your TSH should not be so low with such low doses of Synthroid that you are taking.
What your doctor is missing (and possibly you) is that your T3 is NOT normal. Normal people have T3 at the middle of the reference range (50% of range) - for your total T3 the middle is 128.5 and yours is only 92 which is only 15% above the bottom of the range - that is not normal - that is LOW. Unfortunately a lot of doctors do not realize that. T3 is the thyroid hormone that does all of the work in your body so if T3 is low you get hypothyroid symptoms - such as muscle pain, fatigue, weight gain, and more sensitive to cold temperature like you are having.
Your doctor is also missing the fact that a normal person's body makes 90 - 100 mcg of T4 daily. So to give you only 75 mcg of Synthroid/T4 daily (or less) is clearly not enough! If I was you I would go back to 100 mcg immediately and get new lab tests in a month.
I agree with telus2 that the average thyroid gland secretes about 94 - 110 mcg of T4 daily. Along with that the gland also secretes 10 - 22 mcg of T3, which is vital as stated. When taking thyroid med orally the absorption is only about 80%, so a full daily replacement amount of T4 would require about 120 - 128 mcg of T4 and about 12 - 28 mcg of T4. Since you are taking only 75 mcg of t4 there is no way that will get you to an adequate level of Free T4 and Free T3. This is especially true since taking T4 med only typically results in reduced conversion of T4 to T3. This is why so many patients find that they need a source of T3 in their med to adequately raise their Free T3 level. An adequate Free T3 level is most important since symptomatic change has been shown to be mainly associated with Free T3 and less with Free T4.
If you are going to give the doctor info to attempt to persuade him to treat clinically rather than based on TSH I also suggest that you click on my name and then scroll down to my Journal and give him a copy of the Overview to my paper on Diagnosis and Treatment of Hypothyroidism: A Patient's Perspective. The paper explains all this and provides extensive evidence that a suppressed TSH does not mean hyperthyroidism unless there are accompanying hyper symptoms due to excessive levels of Free T4 and Free T3. That might slow down the impetus to reduce your med when it actually needs to be increased and perhaps also needs some T3 added. And don't forget the importance of Vitamin D, B12 and ferritin.