When it starts to make sense, you KNOW you're in trouble! LOL
Exactly, your whole body slows down, kind of like dragging an anchor around behind you. As you increase and your FT4 levels go up, your body has to do a whole rebalancing act. Conversion has to ramp back up. Our bodies have to heal after months or years of being hypo.
I was on levothroxine 50mcg for over a year before I even realized I needed an increase my ignorant doc kept saying your levels are fine even when they were at the bottom. I've been trying to increase for about three months now. I just started back walking on my treadmill. I think my metabolism must have been so slow that everything I took caused a reaction. After exercising, I'm starting to realize that taking the meds are getting a bit easier. I assume if you've been undermedicated for a ling time, your system is running slow causing medicine or vitamins to not move properly in your body. It makes sense. It just like being constipated. Your body needs your metabolism to pick up. This thyroid thing is beginning to make just a little bit of sense.
Some of us are just very sensitive to the meds. If you're struggling so hard to tolerate them, you could have an adrenal issue or a vitamin/mineral deficiency (especially iron/ferritin). Or you might just have a basic sensitivity to meds. How do you do in general with other meds? Do you usually react to them more or have to take less than most other people to get the job done?
It took me over a year to go from 25 mcg to 75 mcg. I had to take baby steps along the way.
How much and how fast have you increased? Have you tested adrenals and vitamins?