I have the opposite - an over active thyroid. I don't know if they can be directly compared, but I've had mine for 23 years. It wasn't operated on, I was on carbimazole tablets for about a couple of years, it eventually settled down and I was taken off tablets, but it reared its ugly head again a few years ago and, although I was only briefly back on tablets, it's been a bit like a yo yo and has to be monitored from time to time.
Just thought you may be interested in a slightly different perspective of the same problem. None of my family has had this condition. When I was first afflicted with it, and before the medics diagnosed it, I too felt washed out, easily tired, had some palpitations of the heart, and had the shakes as if I was an alcoholic.
It seems like once you have it, you're stuck with it for the rest of your days. Good luck.