First let me say that i don't have much experience with thyroid problems. I did some reading and noticed that it is usually recommended that you taper off the levothyroxine while starting the Armour. Is this what the doctor recommended?
The dosage schedule for hypothyroidism is:
Hypothyroidism—Therapy is usually instituted using low doses, with increments which depend on the cardiovascular status of the patient. The usual starting dose is 30 mg Armour Thyroid, with increments of 15 mg every 2 to 3 weeks. A lower starting dosage, 15 mg/day, is recommended in patients with long-standing myxedema, particularly if cardiovascular impairment is suspected, in which case extreme caution is recommended. The appearance of angina is an indication for a reduction in dosage. Most patients require 60 to 120 mg/day. Failure to respond to doses of 180 mg suggests lack of compliance or malabsorption. Maintenance dosages 60 to 120 mg/day usually result in normal serum T4 and T3 levels. Adequate therapy usually results in normal TSH and T4 levels after 2 to 3 weeks of therapy.
Since you were already on thyroid medication, your doctor may have skipped the initiation and put you at the highest dose recommended because you are having symptoms of overactive thyroid. Read the following:
Thyroid Suppression Therapy—Administration of thyroid hormone in doses higher than those produced physiologically by the gland results in suppression of the production of endogenous hormone. This is the basis for the thyroid suppression test and is used as an aid in the diagnosis of patients with signs of mild hyperthyroidism in whom base line laboratory tests appear normal, or to demonstrate thyroid gland autonomy in patients with Grave's ophthalmopathy. 131I uptake is determined before and after the administration of the exogenous hormone. A 50 percent or greater suppression of uptake indicates a normal thyroid-pituitary axis and thus rules out thyroid gland autonomy.
For adults, the usual suppressive dose of levothyroxine (T4) is 1.56 mcg/kg of body weight per day given for 7 to 10 days. These doses usually yield normal serum T4 and T3 levels and lack of response to TSH.
I am only guessing but your doctor maybe trying to readjust the thyroid activity and rule out thyroid gland autonomy by using the Amour thyroid at that high a dose.
If you continue with the doctor's plan and continue to have symptoms of headache and sweating, etc, please contact the doctor asap as they can be signs of serious reaction to the medication.
I would consult a pharmacist, that is willing to entertain the question, as to what the conversion between the two medications is.