I'm not sure what to do, I can't get any help and just want to say my problems

I'm a 16 year old who has suffered from aspergers, adhd and a lot of other things like anxiety and sensory processing disorder. I have always been bullied and people would always threaten and hit me during school, I've never kept friends for more than a year or two and I'm just going into 6th year in school and all my friends have left and I have no clue what to do with my life. I've never been given any proper help with my mental health issues and I really need and want it. every time I ask for help I'm either not given it or just told that I can't get it, I need long term help and every time I'm given "Help" its just in the situation that I'm in, in that moment and that doesn't help at all. I also get extremely angry all of the time and cannot control it, mostly everything makes me angry, eating noises, any noise pretty much like a noise that shouldn't be there or one that just distracts me. people too, if people are just in my way or doing something that isn't what I expect or want them to do it makes me angry. but when I say I get angry I just don't mean I get a little angry, I get absolutely furious and over the past few years I haven't really shown it in school, I just wait until I'm out of school to express it which isn't good because it's either me shouting at my family or hurting myself. on that topic, I've also suffered from self harm for a long time and can't stop it, I usually use a knife to cut my arms or bite my hand really hard or scratch my arm up and down until it goes completely red and my skin rips off. in conclusion I just severely need help and have no clue what to do. I just feel like at one point I'm going to blow up and do something that I don't want to do and I really don't want that to happen.