Your description sounds like it is an unwelcome set of conditions, but there also may be some clues to what may be underneath it. It is clear you are at a transitional time in your life an you have mentioned at least 6 major changes:
- You are graduating and leaving what you know
- Your best friend is moving away.
- You are about to begin college.
- You ended competitive swimming.
- You are going to live with your sister.
- You are harming yourself with your nails.
Transitions can be very rough on us and any one or two of these would be a lot. You have at least 6. I would let your parents know that you want to go to a physician. He or she will be able to look for physical causes. As an example, the exercise with swimming produces an array of biochemical changes that have been helpful for you. Tell this to the physician and he or she can determine what nurtients, vitamins, medicine, etc., might be helpful in making you feel better.
The point is — don’t wait. I would certainly sign up for counseling when you get to college, but at least get the medical consultation out of the way.