I has a similar experience. I started with Iodine last year after a few years of feeling miserable (undiagnosed hypothyroid), and then a few months of scary symptoms (dangerously hypothyroid), and then one day last summer, I went out for sushi and felt incredible, like a super hero. And decided Iodine was the answer to all of my problems. lol Well it was a lot more complicated than that!
You can probably find my original story from last year on this site if you want to read it.
Are you taking a multivitamin? Any b-vitamins? Vitamin A, C, E? If you are, how much? What form?
If there is one thing I've learned and would pass on from my year of recovery, it is that ALL the vitamins and minerals are important. No one nutrient is more important than the others. Iodine is NOT special. It may just happen to have been what you needed 8 months ago, but now, you are likely low in other things.
Take a look at your supplements and diet, and look for what you're not getting enough of. Even if you're taking it, maybe it's not in a form you are absorbing.
Celiac and thyroid both put you at risk for b-vitamin deficiency. Even just using iodine, and getting that boost of metabolism, puts you at risk.
Celiac and thyroid mean you are likely not great at absorbing any fat soluble vitamin, not just vitamin D. Vitamin D gets a lot of press lately, causing us to forget the other fat soluble vitamins, which are every bit as important. Labs don't have a way to test for vitamin A or E accurately, however, so for this reason alone, doctor's never talk about them. You need them for thyroid function, immunity, heart health, eyes, skin, hair, and on and on.
I've only gotten better from a lot of trial and error with different forms of all the vitamins, and pretty big doses too, and then seeing what helped and what didn't.
Vitamin A made a HUGE difference for me. The same boost as I got from iodine. Then that made me thiamine deficient - from the high metabolic rate. Took me too long to figure that one out. I ended up with nerve pain from low b-vitamins - which I mistakenly thought was from too much B6. So I wasted some months not taking enough B6. Then started on B6 and got hyperthyroid from that - which made me feel amazing for a few days only to crash from low everything else.
And now I'm so incredibly low in thiamine I can't tolerate any Sugar at all, and have had some scary symptoms from that. Now I'm taking a special form of thiamine since I've lost the ability to actively transport thiamine from the gut. I take benfothiamine and lipothiamine and regular thiamine. Some research suggests thyroid problems result in a thiamine transporter problem. I wish I had started taking this "lipothiamine" supplement last year - along with the iodine. Low thiamine causes many problems. Cardiovascular, digestive and neurological. Fatigue and memory problems. Heart problems. Stomach problems including low motility and low stomach acid, which then leads to bacteria overgrowth and reflux, and more nutrient deficiencies from malabsorption.
Zinc is another really important water soluble vitamin. Zinc deficiency is hard to recover from because you can't take more than 50mg or you can become copper deficient. If you have raised TSH for a period of months or years, it will eventually deplete zinc, because you use up a lot of zinc making TSH. And then you will eventually lose the ability to make TSH, and doctors will think your thyroid is fine, even when your hair falls out, your skin breaks out like a teenager, your voice goes hoarse, and you have ankles the size of Texas. So be sure to take zinc!
And Iron - you needs this to make TPO - which is the machine which makes thyroid hormones. So if you take a lot of iodine and it boosts your thyroid production, you could run out of iron for TPO. Then you'll end up with headaches, Depression (because you need iron to make serotonin), insomnia (because you need serotonin to make melatonin), anemia, and a sore tongue, swallowing problems, and exercise intolerance, heart palpitations... etc.
We haven't even talked about proteins yet. But that's another one to look into at some point. Certain amino acids can be depleted in thyroid patients. It's important to get lots of protein because these work together with all the vitamins and minerals.
Hope this helps! Sorry it's so long, it's hard to make it short because it's all really complicated.