* Not a doctor or professional, just rambling as a lay person *

Brains are complex, but seem to boil down to input in, output out. The inputs are sensory stimuli (sights, smells, etc) as well as various hormone and other chemical levels in your body and brain. The outputs are things you think and do.

The brain will use chemicals like dopamine and serotonin to encourage behaviors. Dopamine acts like the “remember that thing? ohh that would be really good right now” messenger chemical, and serotonin is the feel good reward messenger chemical when the task completes.

Those chemicals have to actually attach to receivers in cells to work, and other chemicals can take their spot under certain conditions (this is why caffeine keeps most people from getting sleepier — it takes up the space that the “we’re getting tired” messenger chemical would otherwise attach to).

* Again, not a doctor or professional, just rambling. *

But If I had to guess, some part of that process is not working as expected in your brain. Dopamine not being produced when it should be, or serotonin not attaching when it should be, or something like that. If you also experience symptoms of ADHD or depression and/or your symptoms impede your life or otherwise bother you, you should consider seeing a psychiatrist to narrow down what’s actually happening and find possible solutions.