Just because thyroid test results fall somewhere within the reference range does not mean they are adequate for you. The ranges are far too broad to be functional across the entire range, plus people may have different optimal levels.
In your specific case, since you are having symptoms, I'd say that it is because your ratio of Free T3 to Reverse T3 is too low. Reverse T3 is a normal occurrence when T4 is converted to T3; however, if the level gets too high, then the excess Reverse T3 interferes with normal metabolism of Free T3 in the cells, resulting in hypo symptoms. Even if your Free T3 were raised with meds, to the extreme of its range, that would barely raise the ratio to the recommended level of 1.8 or higher. The ratio is determined by multiplying the Free T3 by 10 and dividing by the Reverse T3.
So, I'm sure you are wondering what might be the cause for excess Reverse T3, and what action is recommended. Possible causes for high Reverse T3 include dieting, low ferritin (iron), high or low cortisol, low B12, stress, low selenium, low zinc, low chromium. So you might want to discuss with your doctor and get some additional testing done. While you are at it, I would request Vitamin D as well. With all those results, you and the doctor can decide if there is something that needs to be corrected by supplements. At the same time you can discuss starting on a low dose of T3 med to try and minimize your symptoms in the interim. Neither Armour or NatureThroid would be advisable because the added T4 would likely cause more conversion to Reverse T3, thus exacerbating your problem.
Reference ranges:
T4 1.26 (.82-1.77)
Free T3 2.8 (2.0-4.4)
Reverse T3 24.6 (9.2-24.1)
TSH 2.16 (.45-4.5)