How can i get over my past?

im 14 and i have a bad past and im getting a little depressed about it all. and i dont really want to see a therapist. is there anything i can do? because i hate this feeling of being sad and honestly its over nothing. my lifes actually getting better. i dont get why im sad now, even though i wasnt sad then when my life sucked. does anyone have advice for me? or any explanation on why i NOW feel sad?