Why do I wish to die?

For over a year, I have felt a desire to die. It's fluctuated between just stopping myself before doing something serious to forgetting about the notion of killing myself for a few weeks.

I don't personally think I'm depressed, I'm just a little sadder than I was before. I don't enjoy things as much anymore, but I can still feel happy; there are still things that bring me joy. Nothing traumatic has happened in my life and there's no real reason for me to feel this way, yet I still feel burdened as if something has happened.

It's not as bad anymore and I used to cut my arms but I haven't done that for over a year either. Sometimes I'm just slightly angry and I want to die. I feel so tired of just existing, but I really don't know why. Does somebody know what's wrong with me? I don't believe I experience more sadness than the average person.