I went untreated for quite a few years. (I'm disabled...lung, prosthetic leg, now bones and kidneys). I think because I do have disabilities it became easier to 'gloss over' the hypothyroid symptoms.
Anyway, I had a good start on T4, and then it 'tapered off' to 'same ol'. Why? Because my body could not convert that incoming T4 into T3 (if your body doesn't convert the T4 into T3, you don't get the energy, and lifting of depression).
It's VERY important to me that my doctor tests BOTH Free T4 and Free T3 (in case you're wondering, T4 and T3 show what's in the bloodstream, but the Free's show what's USABLE, and that's important).
Some people's physicians add synthetic T3 (Cytomel) to their T4 (and most lower the T4 when adding it) and some physicians switch their patients to porcine (pig) thyroid also known as Armour or Westhroid, or Naturethroid. Recently, the Armour available was reformulated and had filler in it, some overcome this by splitting their dose, and chewing it.
I send my Rx to Canada and get Thyroid (same as the old formulation of Armour). A new lab in Georgia is making Armour Thyroid now and they say it is working as well as the older formulation.
Hope that info helps. There is also a great website:
www.stopthethyroidmadness.com for research and information.
I hope you feel better soon, and your doctor will have to closely monitor your heart situation if you DO go on T3, as too much can cause problems with heart rhythm in some.