I also wanted to recommend another website, called Stop the Thyroid Madness, that addresses the issues with T4 only not working and goes into the other options available. It's an excellent site and helped me a lot. Tons of good reading. It has sections on reverse T3, adrenals, T4 only not working, etc. Well worth a look!
Also, have you had your iron levels checked? Its very common for people who are hypothyroid to have low iron also. You could have low iron AND need a change in meds at the same time. Thyroid meds, whatever kind they are, don't work as well if your iron levels are not optimal. If you are having trouble even doing a little walking, I would definitely check this out in addition to the medication change!