I'm very similar, or was. I was diagnosed with ADHD aged 30. If I'm working on something I enjoy or find interesting, I'm all in on it, obsessed. If I find it slightly dull or tedious, I'll have to fight with myself to get it done, just turns into relentless scrolling through hacker news, or get distracted with other things.

The trick, I've found, is to either find ways to enjoy what you're working on if you don't enjoy it. For example, gamifying it or finding some other challenge in it. Or try to insist on specialising on what you do enjoy working on more.

Read the following as well (if, of course you haven't already):
- Flow by Mihaly Csikszentmihalyi
- Deep Work by Cal Newport
- Hyperfocus by Chris Bailey

Oh, and don't beat yourself up for not feeling 100% productive or enthusiastic all the time. Most of this expectation is a tech culture thing and it's just silly. Most jobs don't expect this, most jobs people assume you're sat around talking and eating biscuits several hours a day. Our brains aren't designed to work in well defined, lengthy chunks of time, it's absurd we expect that.

As a few others haven't mentioned as well, it's worth getting screened for ADHD if you haven't already, the meds can really really help. They were a revelation for me anyway.