I kind of have the same "problems" but it's more extreme.

I am totally into something and be very disciplined for a specific period of time and then I lose all interest pretty much over night ... but that's okay.

In my opinion, in the end it all comes down to what makes you happy and you feel comfortable with. Even if most people have one or a few specific things they really like, it just doesn't work for me. For some time I felt like this is a problem but I guess that's just how it is for me.

I had always the same cycle: I found something I thought which will make me happy and told myself, whatever happens I should stick with it. At some point I lost interest but kept going because I promised myself to do so. I got unhappy, stopped and beat myself up about not sticking with it. Not a really health process.

So what I do now is just to keep trying out new stuff, doing it as good as I can and enjoy the ride until I lose interest. I even put a lot of energy/discipline into it when I have hard times but I don't think it's wasted just because I lose interest at some point. It's all about the experience. If by any chance I will find my one true calling that's great ... but I just can't force it and I don't think that's what discipline is about.

For me discipline is more about reminding myself of the motivation why I do something and keep going even if I have a low for some time. I wouldn't recommend to drive yourself insane by being disciplined about something you don't like or not motivated about in the long run. That's wasted discipline in my opinion and more like punishing yourself.

Also for me, it took time to learn being more disciplined. And believe me I am far from being disciplined all the time ... but as pretty much everything, it's a learning process and doesn't just happen over night.