Self-harm and depression due to stress

I am a 17 year old male and I don't really know what could be wrong with me, if I am just overly stressed or if it is something more. I have been under emotional turmoil since about the 4th grade because I was struggling with having a learning disorder (SLD), a new school, and experiencing bullying. This carried on into middle school where it just got so bad trying so hard to make good grades and making D's and F's on top of being called a retard, gay, freak, you name it, that I became very distant from reality and desired to take my own life very much. Now that I am I high school things are better and I am not being bullied but I still struggle with school because I did very well freshman year and was recommended for honors classes. Sophomore year was very hard and I didn't do so well in some classes which stressed me out to the point of having frequent panic attacks, I stopped eating, sleeping, and self-harming (cutting and scratching to be exact). Now that I am a junior, I am under about the same level of stress maybe even more so and I have tried so hard to stop harming myself but when I stress, in my head I'm saying, "I need to cut, I need to cut!". Also, the fact that it is fall makes things worse because I get very sad during the cold times and I can't stand to be outside and I don't know why but when I see the sun setting, it depresses me. I really don't know what is wrong with me, I have done many symptom checkers and they give me depression and anxiety disorders and I have never been to the doctor about this and no one knows about this except myself. Any advice would be greatly appreciated.

Also sorry about the length I just want you to know everything, I just wanted to point out that I am not always like this. Sometimes I am quite happy and content and I feel very confident like I could do anything and then it will change to being upset, angry, confused, suicidal, etc.