Synthroid Detox

Hi, I have been on Synthroid following thyroid removal for 20 yrs. About a year ago, my thyroid levels were out of balance after having always been consistent. My naturopath informed me that Synthroid can lose its effectiveness after several years, and he switched me to Armour Thyroid 6 months ago. My thyroid numbers are now in range, but I am left with residual issues as follows (which I believe are a result of the dwindling impact of Synthroid not working properly):
1. Body temp always feeling cold, greater than normal hair loss, weak nails and weight gain.
Since I started the Armour, I am less cold, less hair loss, stronger nails and lost a few pounds.
2. Rash (red and itchy) on the back of my neck started about 2 yrs ago, worse at night and I have tried many remedies with no improvement. The past month, in addition to the rash, I have felt off kilter - kind of light headed with no energy. I am wondering whether any of the Synthroid ingredients would have caused this. This is my #1 concern.
FYI - I have gone through a very deep heavy metals detox over the past 2 years, I eat clean, work out 5x/week and take no other meds. Now Im just so tired. Had my adrenals tested and just started adrenal supplements.
Thank you so much for any input!