Hey. So this is basically a post asking A. What could have caused this/is causing this and B. Does this mean that I’m mentally ill or need to get therapy
*This post WILL contain mentions of self harm and intrusive thoughts, if you are upset by these topics it’s best that you don’t read

Some info first: I’m -16, I self harmed for 2-3 years continuing to present day rarely. I have MaDD and experience violent thoughts &amp;amp; impulses. I live in the US.
TL;DR at the end

Here’s the run down: I struggled with self-harm for about 2 years, though I can’t remember very well how I felt when I did it due to memory issues, though I know that it was more out of self-hate and anxiety from stress more than anything else. Following that, starting in 6th grade(self harm continued to then and I’ve had large gaps between any sh since then), I began experiencing very violent &amp;amp; graphic intrusive thoughts/violent idealization. 

This issue has continued on for 3 or so years (present time) along with since around the same time: a noticeable lack of empathy for others (though low empathy was already kicking in 5th grade) and an extremely fluctuating view of myself and others. 
Sometime I’ll feel like I’m better than everyone, similar to being manic in a way and I’ll have increased violent urges and thoughts about others or just violence in general. Othertimes I’ll feel like I’m worthless and should die. Basically my view will change from “I’m better and more enlightened than others I could kill them all” to “I’m horrid and bad I should die” both of which are accompanied by violent thoughts and impulses.
I recently relapsed though it was more so out of addiction in a sense and simply the act of cutting. My thoughts &amp;amp; impulses are progressively getting more frequent and “unique”.
Do I need therapy/help? Should I look for a diagnosis of something or should I just chock it up to bad mental health in general.

TL;DR: Ive struggled for about 3 years with low to nonexistent empathy, violent/self harming behaviors, and violent intrusive thoughts and impulses. Do I need help or a diagnosis? What can I do?