Anger issues

 When I was younger, around my teen years my sister would basically just be a bully. I could take it for some time but if she would just bother me with her constant hurtful words, I would just switch to anger immediately. I sometimes got really angry. It was confusing for me and even my family. I can't explain it, it's like anger takes over. Then after it was gone I'd be okay. I tried to express later in a logical way why I would get that anger burst but it didn't make sense to them. I guess we keep so much inside and can take so much insults or verbal abuse, etc but to a certain level. Then we just burst. This never ever happened with anyone else except her. She just pushed all my buttons. After I moved away it never happened again. I choose to be with people that give me peace or just be on my own. This never happened again

Rather than meditation, what helped me more was putting on favourite music but keeping my focus on a layer of it, like the bass line, and then after a few seconds switch to another layer, and go back to it when thoughts get in the way.  Its mindfulness, rather than meditation - our brains can't focus on senses and thoughts at the same time, so its one or the other, if you want  a break form thoughts then focus on music, or other things you enjoy. The focus bit is the important bit, just listening or doing things isn't enough, you have to force your brain to focus on what you are hearing, seeing, etc.     

The 2 most common things I've found are: 1. Unresolved issues. 2. Sensory assault. 

Both of these require a bit of mindfulness, awareness, and active participation to address and fix. I would suggest taking on one thing at a time.

Letting go is not an easy thing. We need Resolve. That can mean a great deal of effort in learning about relationships and human psychology. I've found books can help. Getting a mentor and a therapist can help. Learning how to protect and care for ourselves - assert boundaries and identify what is abusive. Autistics tend to experience a great deal of injustice.

Writing everything down and filling notebooks can actually help. But I might even suggest presenting some things you went through here in this forum. You might find many of us have gone through the same and sometimes being affirmed and feeling connected to others with similar experiences who recognise what you went through can have a profoundly healing effect.

Meditation can cause difficulties, because you might open up room for thoughts you normally keep at bay, and so best to learn to manage difficult thoughts first.  In a similar way, just trying to relax can cause autistic people a similar effect.

To be less angry you have to learn to react less to what makes you angry, choose a less angry response, you can just be annoyed instead.  You might want to try an anger management course, or self-help book, because just trying to be less angry doesn't really work, you have to understand what the triggers are and why you react to them with anger. 

Anger is a normal response if pushed too far, but you are angry too much or for slightest reasons then its the wrong response and something to work on.

Painful events can cause anger issues, so therapy might help.  People say about letting go, but its not that simple as brains just don't let go, its more a case of learning to hold on to better things.  Brains tend to feed us what we already expect/believe, you have to let your brain know what you don't want, by expecting/believing something better/healthy.

How exactly does mediation make you anxious? I'm trying to find a possible connection if it's the way I interpret your description.

Mediation (focusing the brain), playing chess, painting, writing a novel, translating etc. where I use my brain in a more cognitive state, thinking/comparing/finding solutions... leads me into a depressive state that lasts for 2-3 days, before I normalize. It's like my brain is not built to think like that or restricted, and when I force it, it ends up with wasting all my serotonin.