Hi lae,
I believe what you are experiencing is a reaction due to anxiety, which is caused from the stress in your life. It doesn't sound like you're too depressed, just unknowingly anxious. My best advice would be to try and realize when you're performing this habit, and consciously tell yourself to stop. Maybe even try finding something that you like to do that will relieve your stress and cut down on your anxiety, like hanging out with your friends or excercising. That way, you'll be keeping your anxiety down, won't be picking at your skin, and be self-healing!
Best of luck!