It sounds like you’re dealing with a lot of stress and anxiety, too, if you’re on a “hair trigger” with your emotions. Some self care and/or therapy may help with some of it, but you sound like you’re on the right track already. Try to be aware of when you feel that way, try to identify why the situation makes you feel that way, ask yourself what you can do in that situation too change anything, and try to view the situation from other perspectives (doesn’t have to be from the perspective of the person making you angry, but can be a stranger viewing the situation from the outside).
Best of luck to you! And keep in mind that by just wanting to improve yourself in this way, you’re already take a step more than most people!
For the second situation, it isnt always that they want to be asked the question. Sometimes they noticed a change in your behavior recently and are checking in on you.
Example, you’re eating lunch and you love chocolate pudding. You usually eat your chocolate pudding every day without fail. Today, you didn’t eat your chocolate putting and just left it sitting there.
A: “Hey” B: “Hey” A: “So… what’s up?”
Regardless, “what’s up” is just a place holder for “how are you”. Sometimes that is just small talk and a way of fulfilling simple social interaction, and sometimes it is a question with genuine interest in knowing what is going on in your life (or asking you first, so they feel comfortable sharing what is going on in their own life).
I always find it easiest to give a simple and short, but honest, response, and elaborate further if they show interest with follow up questions. Of course, giving them information you are comfortable giving that person.
A: “What’s up?” B: “Not much, I’m a little tired today. You?”
or
A: “What’s up?” B: “Kind of sad, but I don’t want to talk about it.”