What causes me to get so nervous, moody, grouchy, and anxious? and Emotionally unstable?

You sound like me. Maybe it's the age you are at, so your behavior and way of thinking is quite normal. You're just missing out on important aspects of life or lacking experiencing certain connections with individuals. Maybe you are going through stressful times which is making you act out in such ways. You just need a change in environment and people. Once you figure out what you want and have established that you'll be happy.