12.5 mg is a good "maintenance dose". Unless you are battling an urgent health issue caused by a bodily shortage of iodine, there is no imperative to change that dose. Also you are doing well to be taking the companion suplements to insure that your body makes best use of the iodine.
My Iodine journey is like that of many other people. Here on this particular forum you have many who have had great results from iodine, and consequently think it is the best thing ever, and come here to tell everybody about it. Most people however don't have as marked an improvement. And you can find them elsewhere on the web saying that they discovered iodine, Iodine has helped them, and that they take it regularly.
My initial response (first two days)to Iodine was positive. Then I had negative symptoms including some mild thyroid swelling for about 2 weeks before my body seems to have adjusted to the higher intake of iodine.
Many people stop iodine supplementation when they notice negative symptoms. Often they will breifly try again later and notice the same negative symptoms, and ever after they are on the web claiming that iodine supplementation is bad for you.
Thanks to the related experiences of many people on here who freely share their annecdotal evidence along with what little other research has been done, and historical practice, I was educated enogh to continue on supplementing iodine. I believe my health has been gradually improving as a result of my efforts to supplement iodine and other trace minerals, better balance the major minerals, treat myself with herbal supplements, eat more vegetables, and weightlift.
I now feel healthier, look fitter, function better, and accomplished all that despite growing older.
On a seperate note: If you are of average intelligence or above do not trust doctors. Much of what they "know" is wrong. You will find better and more recent information on the web than they were taught in school, and you will find out about options that their profession will not be talking about except to reflexively dismiss. The scope of most doctors practice is myopically focussed on patented drugs and surgery.
If however, you are of low intelligence, then you will likely not be able to filter through all the bad information on the web, and are actually better off listening to doctors than figuring out your own treatment.
I trust you'll make the right decission or live with the consequences.