Theory 1, there is something you value more than all the things you're doing that qualify as 'interesting' like for example, self esteem, validation, societal acceptance, filling an unknown void formed long ago deep in your psyche.
The addiction to suffering or pleasure in pain maybe is rooted in deep seated shame, self loathing, self blame, or a desire for control. It could also be a habitual pattern engrained from years of some form of mental, emotional, or physical abuse or traumatic experience(s).
I'm no psychologist, but this is likely a good entry point for some deep inner searching.
I thought I'd already been down that road myself, and then I did therapy with people who were far better at introspection than me (trained professionals) and I discovered a lot that I hadn't already known (though I thought I knew everything there was to know about myself).
It's not really about how much time you spend trying to figure things out, because the mind doesn't go, "ah yeah, ten years is long enough, probably done figuring myself out now." There is no completion date for such a task, and I would argue its a continually evolving process...
For example, sometimes you are ready to see something, sometimes you are not. It's not about time, as much as it is about, just how the mind seems to work, most of the time....
I think noticing symptoms like chronic boredom or emptiness is sort of scratching the surface, in my opinion. It's like, you know somethings not right, but you can't put your finger on why. Somethings caught your eye as a potential, clue. I look at these 'tells' or 'clues' as 'leads' into a deeper, port of development and self discovery? I guess you.... could say.
What you're experiencing is likely very normal, and try not to be hard on yourself about it, as we all are just human. Sometimes it can seem a little complex, but it comes down to our basic needs, primal drives and instincts, and survival most of the time.
A trained professional would likely help you ease into this process of self understanding in a way that, is not too terribly uncomfortable or threatening. Though growth of any sort or healing can sometimes be a bit uncomfortable, it's far less scary than it feels looking in from the outside....
Also, it's okay not to have it all figured out... I used to stress about it like it was a goal to, find all the answers, solve the problem like a math problem, and be done with therapy in 1 year. But therapy is more like, working out. When you stop doing it, you get out of shape. You're never 'done' working out to remain in good shape.
the treatment for optimum mental health is sometimes continual exercise. the best thing you can do for yourself is, be totally honest and raw with yourself as possible, diving deeper and asking why, as much as you have the opportunity to.
so, we start with. i feel chronically bored. i would say, to myself then, "why?"
however a professional would know whether or not you're ready psychologically for that question, or in the best place for it... sometimes other things are more important first. kind of a stabilization period. before you get too deep in the inner work.
introspection is never ending, you're never finished. you're always still learning, sometimes about yourself, and evolving.