Why do I feel so sick every day if the pain is not that bad?

I've been having daily head pain for... Two years? More? I'm not sure. It's not debilitating, it feels like having back pain every day, except for when I get a painful attack.

So why do I feel like I'm living with chronic fatigue every day? I have limited energy, get tired easily, can't think properly most of the time, never want to exercise...

I got Vyepti and I'm sure that's contributing to my fatigue, but I don't know, maybe there's something else going on with me. I know intellectually that chronic pain can be debilitating because it tires the brain out, but I really feel like I should be able to do more. Like maybe I need to force myself to do stuff, and that will give me more energy in the long run?