That's so wonderful that you feel so much better! Yay! I too felt tired and blah when I was hypothyroid, and my weight just kept creeping up. When I started taking some supplemental thyroid hormone (I think I took synthroid), I felt so much better. I do think that of all of the different kinds of prescription meds that people take, taking supplemental hormones in a case like this is a great option. It's just something that most bodies make anyway, and it doesn't seem like it will be a burden on your liver to detox. And hopefully you will heal yourself in time and not need it for the rest of your life. I'm really hopeful that you can beat this thing by going gluten free. It's awesome that you are willing to try it.
Reading your questions about reading labels took me back to the first days of being gluten free. I was overwhelmed and didn't know which things on the label might be harboring hidden gluten. Here is what I recommend: get a good book on being gluten-free, or perhaps just peruse some of the celiac support websites so you can learn all the things that might indicate gluten. Eliminate as many items from your diet that list ingredients that are mysterious sounding and try to focus your diet on plain foods and packaged foods that indicate they are gluten free. For the packages that don't say gluten free, you can always call the companies - they always have a phone number you can call. I called several companies in the beginning to confirm for some items that I had in my pantry already, and the people whom I spoke with were really nice and helpful.
You don't want to deprive yourself too much since you are already letting go of lots of things, but if you can be happy eating plain produce and grains and beans, you won't need to check anything. But for all the things that you really enjoy and want to keep in your diet, make calls if there is anything suspicious.
I have to confess that I don't actually remember about maltodextrin - I think it's okay and made from corn, but I'm not 100% sure. I don't eat stuff like that anymore so it's not an issue for me. I eat plain produce, gluten-free grain and beans. I have vinegars, some pure herbs and spices, nuts and seeds and even some olive oil (which I haven't used in a long time but have for guests), and I just don't eat most things that have more than one ingredient on the label anymore.
But that's just me and how I like to eat very simply. You don't have to go that far in order to be gluten-free, so don't worry if that sounds like way too ascetic for you. But you will have to do more research and checking if you want to keep consuming packaged foods. And I recommend that you also call if your vitamins and supplements don't specifically say gluten free. Oh, and herbal teas too. You only have to call once and then you'll know.
Here are some things that have gluten that you might not think do: beer, soy sauce, blue cheese, regular oats. And I don't buy things out of the bulk bins at my health food store, even though it's much cheaper and I'm always tempted. Also, when you go out to dinner, be sure to tell the server that you have celiac disease and that you absolutely can't have gluten, so no wheat, rye or barley (or spelt or kamut or farrow) and have them help you figure out what you can order. And when your food arrives, inspect it carefully - several times, especially when I was in France and they probably thought I was just being a picky American woman, they brought the dish with the gluten thing on it anyway! And once (in the US), I saw that there were crouton crumbs on my plain salad, like someone had put them on, then saw my "no croutons" request, and just picked them off again. I always speak right up and am nice but firm, because this is a serious health issue, not just some dietary preference.
Okay, hope this is helpful. Just know that it feels overwhelming at first, but you get the hang of it and learn which products are okay and find your way and it gets easier and easier as you go. And hopefully you'll be healing your body too! You may want to do some research on the internet to find the studies connecting gluten and autoimmune thyroid disease (and diabetes! I'm always so thankful that my body didn't manifest that one) for inspiration.