Family problems: how do I fix this?

Have you tried telling your parents (calmly) how it makes you feel when they talk to you like that? Tell them that it hurts you to see them disappointed in you and upset with you, and ask them what you can do to make it better. It's possible that they may not even realize they're doing it. I would also recommend that you ask your parents to go to family counseling with you, and possibly even get some counseling for you on your own. From what you wrote here, it sounds like you have a lot of anxiety and you need to find a healthy way to deal with it. A therapist can definitely help you feel more in control.