I think the key here is compassion. From what you describe all your anger is directed at yourself. I know it is "easier" to turn it inward. I've self-harmed in the past and been furious with myself too. Partly it's the depression and anxiety playing out, but there are also reasons for what you are feeling. Things get triggered. They aren't just there because you are a bad or defective person. You can begin to manage the feelings even without knowing what the specific reasons are. (ideally you can figure that out too, but in the meantime...) You need be as kind to yourself as you can be and yet set limits with yourself as well.
It is not ok to self-harm. It helps contain the anxiety, while providing only temporary relief. I don't know how to explain, but sometimes I have to talk to myself like I'm a 2 year old in a tantrum. Set limits. Acknowledge the frustration, pain, and fear. Accept the feelings as natural and normal without judging. Sooth and calm.
Piece of cake. Not! But it works with practice. I'll try to find the lessons on dealing with this so I can point you in a more helpful direction. Just for now... please try to be kind and remain hopeful. It can get better. It does get better, but there is work involved and you are totally worth making the effort.
I'll try to get back with that information, but have to take a sick cat to the vet right now. I'm glad I checked in though and saw your post. Hang in there Super Girl. ~m