In time it will release, you can't just "let it out" consciously like someone said. Repression is a subconscious process and suppression in a conscious process.
Talking with someone, especially a therapist will slowly allow you to access the repressed feelings. After traumatic events it is very normal to repress, as this is a defence mechanism, which allows you to cope in the short to medium term without having to deal with the trauma.
The mind can't handle too much emotional distress in one go, hence why it is stored, and bizarrely as you know it can manifest itself physically. This is akin to somatization disorder.
It is good to release the anger in a safe environment, say with a therapist. The reason a therapist is so good to release it with is that they can help you deal with it, and they won't judge. It is very normal to be angry after experiencing the loss of someone, especially a son.
In time it will release, just try not to push the emotions back down when they surface, as this can cause more pain in the long run. Just get used to feeling difficult emotions without panicking, I have learned to do this with practise.
I start off by naturally bracing and wanting to repress / suppress the emotion, but I catch myself doing it, and I often go and lie down and relax in bed, and then slowly let the emotions to release, by just allowing myself to feel them without fighting them. They then release much quicker.
I found this part of your question interesting "How can I stop repressing how I really feel without becoming a hermit or just being angry at the world?" You are implying that you want to stop being angry, but ironically wanting to stop this anger IS suppression. So don't try and force yourself in to a "better" state, as in reality it will be short lived. REAL healing is allowing yourself to "be", i.e. just let yourself feel whatever you're feeling without fighting. I'm not saying it's easy, or always possible in some settings, but I would recommend doing this.
A lot of depression is repressed / suppressed emotions.
I hope your road to recovery gets a little easier each day, week etc.