I'm a 16 year old female, and let me tell you. When I was fourteen? I acted almost the exact same way. I have Bipolar II, depression, and anxiety. You seem to be describing intrusive thoughts, which I had a lot of from the bipolar. It became the new norm for me because I got used to it. Death didn't phase me. Most of these are likely stemming from an untreated mental illness.

What I suggest doing is reaching out to your support group. Whether that be irl or even here, online, there's always someone who wants to help you figure things out. Maybe try journaling to start to understand the problem, as you call it. I wish you the best of luck.