We all know how stressful life can be, so if the stuff is causing issues for you; then it's not 'pretty average stuff' - we're all different and handle different things.
I can understand about how you feel not wanting to burden your mother with your problems; I am the exact same with mine and she gets upset I don't talk to her more. She knows nothing about my issues or therapy or anything. Have to tried explaining to her about why you don't speak to her? Sometimes it can just feel like rejection until someone explains why.
How are you finding DBT? I am also going through it at the moment. Are you finding the skills helpful?
Take care *hugs*
x Katie x