Teenage thumb sucking help?

Some people would consider me a closet thumb sucker, only behind closed doors and never in public. Everyone in my family thought i broke the habit at age 7, but i reacquired it at age 13. Now i'm 14 and i just stopped again, but now im constantly biting my thumb and fingernails. I've never had any sort of trauma and i don't think there's anything wrong with me, so don't suggest that. I just want to know some ways to ween myself off of this. It may be stress, but i dont have anything going bad in my life right now. (By the way, the thumb sucking started when my sister that was a year older than me stole my pacifiers for herself. It was also something that helped me sleep. On top of that, i would rub the edges of a blanket that my cousin gave to me when i was born.) Please give any suggestions other than sarcastic, rude ones. Everyone has their issues, so don't pretend you're perfect.