The definition of hobby is, 'an activity done regularly in one's leisure time for pleasure.' So when it is no longer a pleasure it is no longer a hobby.
It's perfectly normal for what starts out as fun and a hobby to become a chore or anything else you want to call it when it is no longer a pleasure. Common sense should tell you that when that happens it's time to get a new hobby. I've had dozens of hobbies in my lifetime. Some short lived and some enjoyed for many years before the attraction waned.
It could be that you are simply not old enough and haven't had enough hobbies yet to know that it's no big deal when you lose interest in a hobby. You just move on to something else for your leisure time.
That brings up another point though. It also sounds like you may not be giving yourself enough leisure time and not know how to relax. Needing 2-3 weeks to relax is not a sign of a well balanced lifestyle. It may be a sign of a common problem people have but it isn't a sign of a good balance. You should be able to 'shut down' and relax at any time as far as I'm concerned.
I actually have a little ritual that just developed over the years. I can be busy doing chores or a renovation project around the house etc. but every day there comes a point when I say to my Wife, 'I'm done'. When I say that, she knows there is no point trying to even talk to me about anything serious like when am I going to touch up the deck stain or whatever. I'm done for the day and I 'turn off' all that. It takes me about 30 seconds to go from task focused to totally relaxed. And believe me, if there was ever an A-type person it's me.
It's surprising how we condition ourselves to behave in a certain way. But if we know it is in fact just conditioning (habit) then we can if we choose to, change that habit whatever it might be. The common example used is writing. Everyone has a natural tendency to do things with their right or left hand. If you're 'right-handed' you will tend to write with your right hand. But it doesn't mean you cannot write with your left hand. If you lost your hand in an accident, you could learn to write, use a screwdriver, etc. with your left hand. The only question is, what would it take? The answer of course is time, practice and persistence. The same is equally true of learning how to relax, unwind, shut down. It's just a habit and if you want to you can change it.
But first you have to recognize it, recognize you can change it and decide to change it. Then it's just a matter of time and persistence. When you sit down to watch a tv program or play with the kids and suddenly remember you forgot to change that light bulb in the spare bedroom, instead of getting up and going to change it you have to tell yourself 'NO, I'll do it tomorrow.' The first time you do that you'll probably sit there for the next half hour just itching to get up and go change it. The second time you do something similar you'll still itch to get up and go do it. The third time, the fourth time, the fifth time, the sixth time, etc. But eventually, you'll think, 'No, I'll do that tomorrow' and your attention will go right back to the tv program or playing with the kids. Eventually, you will have learned to relax and that will then be your habit.
FIRE will NOT teach you to relax or give you more leisure time. It will simply give you more time to do whatever you do now. If you can't 'turn off' now, you won't turn off then. Look at all the normal 'retirees' who retire at 65 and spend all their time doing things around the house etc. They're still working as many hours as they ever did, just not at a 'job'. You may know some older relatives like that. My neighbour is a perfect example. He's up at 7am and doesn't stop doing 'something' until 7pm every day. He can't 'shut down' and I'm sure he tells himself, 'that's just the way I am'. It's the way he is conditioned to behave, it is not the ONLY way he can behave however much he might believe it is.
