That's great that it's under control SassyGirl
It's one of those things that can be quite tough to do in many people - get that normal level! But it can and should be achieved, and once it is, you should be right!
Hashimoto's.. you're testing me here! It's an autoimmune condition, so basically your own body decides to attack your thyroid for some unknown reason. To start with, you sometimes get symptoms of overactive thyroid because as the thyroid is attacked, it panics and releases more thyroid hormone than usual. However, most people don't notice until it enters the second stage - when parts of the thyroid have been destroyed and you become underactive.. with all the symptoms you described (tiredness, trouble losing weight despite decreased appetite, muscle/joint aches, depression, thin/falling out hair, etc). You will need to be on replacement thyroid hormone for life, most likely. It can take a while to get the dosage right because if you catch it early, your thyroid might not be done being damaged yet! Unfortunately there is no cure, but the symptoms can indeed by controlled by adequate medication.
Does that help? My memory of Hashi is a bit fuzzy, so I hope that's right