I overthink things way to much, fear something bads going to happen, cannot take a joke. PLEASE HELP?

im currently in high school and going through a problem that's hard to explain, being in school is kind of scary thinking of all the shootings in school such as the columbine tragedy and when i say something to someone i think their going to commit suicide or shoot the school,another think is i love the beatles and i was made fun of sopre year(currently a junior) pretty badly and i didn't bother me so much, now it really bother me even if its a kid i know just joking but he does it everyday just to get me mad and laughs about, then when i confront him he's like ' i love the beatles what are you talking about' he like plays tricks with me. it pisses me off but i don't show it, so every time i listen to the beatles i always think of school and what people say and i hate SO MUCH it makes me pretty down and out. another thing is if i watch the news and see like a murder or something i think it's going to happen to me or i might even do this one day when i know i won't. it all goes back to when i heard about columbine and that quote 'It will never happen to your child' used in a sarcastic way im sure. then i would think what if i become that or so. i also have ADHD and the kid in columbine has that so i instantly think im going to become crazy or anyone else with ADHD. i started getting paranoid in 8th grade.but its getting worse,it comes and goes. i tried smoking marijuana to calm me down and it worked really good i never cared what people said or anything. but when i stopped it all came back if worse though, sopre year was the rough one but i never let it bother me until the summer i tried weed, and junior year i stopped and im starting care for the littlest things. is there something i have? am i alone? please help and explain to me steps to help my problem thankyou very much