Well, i really think that you would deeply benefit from some CBT ( cognitive behavioral therapy ) it will really help in making you see things from a different perspective. Next you should really start doing some exercise, a sport to really get everything out of you and focus your anger and frustrations on that, you really need to keep your mind busy with other things so that it does not have time to focus on all the bad and useless things that don't get you any benefits. Don't be afraid or feel shame to seek help, we all need it and sometimes it's the best thing we could do even if we postpone it until maybe it's even to late.
It maybe sound stupid but this is the best and only solution in my opinion and from my experience, keep your mind, body and yourself busy as much as you can, leaving your mind to less time to focus on the things you are feeling and expressing now. You will be so tired at night that you won't literally have the urge or time to think of these things. Please do also consider some CBT management, it will really help.