I self harm with scratching and i didn't really break skin, there is a part that is a bit knicked but nothing major and the day after it felt really sore and im worried about it , what should i do?

If area seems to be infected due to pain , redness, and swelling, would see dermatologist for proper eval and tx

First be sure you use antiseptic on the scratch to prevent infection. Have a physical exam by a Dr. to know if you have a physical illness. If cleared consult with a Clinical Psychologist with expertise in multiple types of psychotherapy to help with what is causing your self harm & a Psychiatrist for medication.