Angry

I am apparently an angry person. I didn't really know, but this is what I'm told.
Anger has never been an OK emotion for me to feel. I'm terrified of explosive anger, and the seething silence that comes before it. I hate conflict. It scares me, stresses me out and exhausts me emotionally. Most of my life I've held in anger, told myself I didn't have a right to feel it, told myself it was wrong and dangerous to express it or even have it. If I am angry, I go silent until I can't handle it anymore, and then I hurt myself or act in a rebellious way. My anger rarely comes out straight, in a healthy way.
Today I've been feeling depressed, and recently I've broken some rules. My therapist told me that these are both symptoms of suppressed anger. I wonder who or what I'm angry about. I wonder why I'm hurting so much inside, wny I want to hurt myself or rebel and hurt some one else's emotions before they can get to me. I think some of the answers I know, but I'm afraid to own them, afraid to really allow myself to be straight-up mad even if it doesn't make sense. In my mind I have to have a really legitimate reason to be upset. If the person didn't mean to hurt me, do I still have cause to be mad? I struggle with that question, because many of my hurts come from well-intentioned people. Many of my resentments are at circumstances, myself, or even God. What do I do with that?
Is there a should about anger? I've always thought there was, but maybe I'm wrong. Maybe there's no such thing as a right to be angry. Maybe if you're hurt you're hurt. Can you have feelings for what seems like silly reasons, or does everything have to make logical sense?