What happens is that the external thyroid given, affects the feedback loop from the pituitary. If the external dose is too high it shuts off the thyroid suddenly. This shuts off the small amount of T3 your thyroid makes too. It is rather a BOOM physiologically.

Endos typically start people off (especially older patients) at 25mcg for a month or two. Then raise slowly. I was at 50mcg when an ice storm hit here and we lost our power for 4 days!
I went into a "crisis" because of this (COLD), and hubby called the endo and he raised me to 75mcg. That seemed to work, and at that dose is where I am today. I had a goiter on the right side of the gland and that slowly returned to normal.

When cold weather hits each fall I have an adjustment time of about 2 weeks. But it is not like the crisis was, that is for sure.
The only residual hypo problem I have is cold intolerance when it is sudden...my legs seem to get very stiff and stairs are difficult outside.

You need to get your Vit D tested. I've had no colds or flu or bronchitis since I started raising my levels. I get the beginning of a flu--the aching part but no congestion or further symptoms.

I'll share this story with you... A cousin of my husband's from upNorth was a nurse, and her hubby a internal medicine doctor.
She was a smoker, and developed throat cancer. She went to Johns Hopkins for a radical chemo radiation, and when that remission happened her thyroid was damaged. Her doctor put her on 100mcg of Synthroid and she and her husband came upNorth (where it is isolated and difficult with no electricity or phones, etc), and she had a terrible reaction to the Synthroid.
They packed up and left after a few days, and when I saw her she was a mess. (lots of heart palpitations etc) That is when she told me, and I explained to her what was going on. At least that calmed her down a bit.

So starting up on thyroid should be a gradual process so your body can adjust to it. This is why I was surprised at your 100mcg dose. Really that is not the way to do it.
But both of them were medical people, and didn't have a CLUE!