I've been on Levothyroxine for years due to an under-functioning thyroid. The meds are truly the only solution and work great once the dose is adjusted correctly. I would never consider going without it.

Very-very-very common. And an easy fix with Levo. Why dragging your feet? Nearly 50% of the population has this by mid-age, a huge percentage of women develop it as a result of pregnancy, and, yes, chemo can initiate it, too. Therapy is hormone replacement, and not necessarily some lab-created chemical; Armour is a naturally derived thyroid hormone, if it makes you feel better. Levo and others are synthetic, which I take.
On the off chance you're mentally aligning this development with your cancer, don't bother; chemo is just one of many many ways to develop hypothyroidism that affects nearly half the over thirty population. You're in good company, my friend.

((Hug))

My doctor(PC) keeps me at 1.0, I believe the new high has been changed from 5.0 to 3.5

Mmm, you ladies might ask to be retested, as they should when first put on thyroid replacement. Mostly dosing is such that they fiddle with it until they find your particular therapeutic dose, and the only way they do that is through a phase of testing. Plus, when the thyroid is crapping out, it tends to do so in fits and spurts- what dose worked once may not always work, hence the retesting schedule I’m sure they’ve set you on. If you’re still feeling lethargic, retest. You want your TSH to be between .5 and 5.0, and some endocrinologist’s shoot for a narrower field. Replacement therapy should be adjusted to bring you into this range, and adjusted again if you fall out of this range.
https://www.verywellhealth.com/understanding-th...(Phone number can only be seen by the question and answer creators)

((Hug))

Plus I am 7 yrs cancer free