Your professors are there to help you - they aren't out to get you, no matter how it may seem. Realize, however, that some of your superiors may be oblivious to your concerns and may forget how it feels to be critically evaluated. Negative feedback does not always mean that you are wrong. Try to evaluate the comments on your work objectively, and then make a rational decision about whether or not to open a discussion or a debate. This is important.
Women are more likely than men to believe that negative feedback is justified and keep quiet.
Don't internalize criticism. Feed your self-esteem bank. You'll soon realize you have what it takes to make it. Remember your successes. Remember that time will help you feel more confident.