Useful one here for you if you are on thyroxine. Researchers suggest that people with poor gastric absorption (ie. low stomach acid) don’t absorb their levothyroxine as much as they might and therefore levels of TSH, T4 and T3 could well be compromised. Giving Vitamin C seems to help:
Effect of Vitamin C on the Absorption of Levothyroxine in Patients With Hypothyroidism and Gastritis
In patients with hypothyroidism and gastrointestinal pathology, vitamin C improves the abnormalities in serum free T4, T3, and TSH concentrations. This approach is helpful in the management of these patients.
The dose given as far as I can make out was 500mg Vitamin C, but it was given with acid. In other words, correct your low stomach acid and take extra Vitamin C if your thyroid meds are not working as well as they should be.
Also, do consider your adrenal function. Often, I have found that people’s thyroid function won’t pick up until their adrenals are more balanced so they have to do adrenals first, then thyroid. I have written a whole chapter on this in the Adrenal Plan if that might help you. Surprising, actually, how often that crops up.