Subway's advice is real get shlt done type stuff. That's the only thing you can do when business must be handled.
For situations that are more... flexible, consider embracing it. Not the inability to focus itself, but what it is telling you about you.
If you're having trouble focusing on something, it could be because that thing isn't for you. Sure, if it's important paperwork or some necessary thing, you may need a "life hack" like exercising to exhaustion an hour before whatever task you need to accomplish. If you're trying to read a book though, because you're thinking "reading this will be good for me", and your brain just isn't having it...maybe play tennis, shoot a basketball. If you can't focus on looking for a job...stop doing it online, walk/drive around and do it the old fashioned way. I can't focus on things that suck, but I can obsess over things I enjoy.
Embrace being you, use more of your energy figuring out ways to make that work and less of it trying to change. People don't really change, much.
This might be terrible advice, I'm a grown @ss child of a man, but I am relatively happy and recently upgraded to a "silver" health insurance plan.