I think there is something mentally wrong with me, help!?

First off, I should tell you that I'm currently 14 years of age, and I'm turning 15 this month, and that I need some help. I feel as if I'm going to go insane. Becuase I'm having impulses to hurt people. For example, I'll pick up a knife, and the first thought that comes to my mind is stabbing someone or something with it.) I also don't seem to show the correct emotions when something bad happens. Becuase, I've seen many videos of various people committing suicide or getting killed, and, I'm honestly not affected by it, I show almost no emotion(s) whatsoever. I'm also told by many people that I'm really shy, (I rarely talk in school, but I tend to talk a little more while at home,) and I also self-loathe a lot too, ( like I'll tell myself I'm a worthless piece of sh*t, that I'll never amount to anything, etc.) I was depressed a couple months ago and I was planning on killing myself, but I ended up telling my mother and she put me in therapy. (The suicidal tendencies have gone away since then, but since come back every once in a while.) I also don't really know if this makes any difference, but, when I was younger (maybe when I was around 7 years old,) I would kill bugs for no reason. I would like catch a firefly put it on the ground and then stomp on it until it was dead, and another time I caught a butterfly and tore its wings off too. I come from a good family, and I have no idea whats wrong with me. All I want is for someone to tell me what possibly might be wring with me before I do something stupid and land my *** in prison.