I completed an MFA in creative writing many years before I was diagnosed with Inattentive ADHD. I struggled terribly with both of the problems you describe. I was so sensitive to criticism that I’d go home and cry after every workshop. I’m still very sensitive to critical feedback, even though it’s necessary for writers. I’ve found that just knowing that Rejection Sensitive Dysphoria is a real thing has been enormously helpful. Now I don’t feel like there’s anything wrong with me. It’s just who I am.
There’s so much “baggage” related to creative work. It helps to journal to get to the root of how you feel about your work. We all worry about failure, but there is a lot to fear about success as well. Try to remember that your work is part of you, but not entirely you. When your writing doesn’t work as well as you’d like, or you are criticized, it is the work that has failed, not you. Try to picture it as something small and entirely separate from yourself. I write in 15-30 minute increments. Sitting down for only 15 minutes doesn’t feel threatening or difficult. Once I’m in front of the computer I often I lose track of time and end up writing for an hour or more.