You just want to be yourself. You want your family to back off. This guide should help you out.

[edit] Steps

Think. What are they criticizing you for? Write down all the reasons. Believe it or not, you may be the one at fault.
Review your list. Is there anything that you could improve yourself on? If you try, there may be a considerable smaller amount of critique and even some constructive information on how to change for the better.
Gather your family for a meeting. This may sound cheesy, but it is important. Firmly tell them how you feel. Let them know that you want them to stop complaining, and that you think you are trying your hardest.
Whenever a family member must make a comment, if you think there is some shred of reason, calmly ask that person how they would improve if they were you.
Be confident in what you do. Keep your head high, and speak surely. This will give your family the knowledge that you know what you are doing, and that you are responsible for your actions and mistakes.
Do not lose control of your anger. Doing this will only make your situation worse. Instead, if a family member is taunting you to no avail, tell them to stop. Ask them to think about how hard you are trying. Do not be a smart mouth, however.
Ask your family members for advice. This will make them feel important, solve any problem you have, make everyone happy, and create a stronger bond.
Be open. If you shut yourself into your room all the time, this will make your parents concerned, thus causing them to ask more questions, criticize you more, and put both sides in an awkward relationship.