HI EVERYONE ---I NEED HELP!

hello, I am 17 years old and have been biting my fingers for over six years. First I would only bite my left pointer finger, which is now extremely ugly and discolored. Now I bite all my fingers. I constantly do this, probably like 30 times an hour. I also use pencils to take skin off in order to make it easier for me to eat the skin. It is getting really bad. Sometimes I take so much skin off my fingers bleed without me noticing, until I get something dirty with my own blood, but seeing it bleed gives me an intense satisfaction. I am also constantly looking for skin to be peeling off. I bite the top of my fingers and the back of my fingers where the skin bends. I also started peeling skin from the bottom of my feet with scissors. whenever I see a little piece of skin coming off I immediately pull on it until I can cut it off. I also constantly crack my fingers probably every two to three minutes. whenever I am biting my skin off I am cracking. My left thumb does not crack as much anymore and hurts when I crack it. Everytime i crack my fingers but cannot crack that finger, I get really bad anxiety and NEED to crack my thumb. I will bend my thumb in many ways in order to get it to crack . It usually takes around 10 minutes for it to crack and during that time I start getting really warm and almost can't breath, the only thing i can think about it cracking my finger. I also start shaking or rocking back and fourth while i wait to crack my fingers. Lastly, whenever I leave a place, I ALWAYS have to walk back and check if I left anything around three times. Sometimes I am in class get ready to go look around to check if I didn't leave anything then walk out of class and come back to check realize I didn't leave anything then walk out again and I can't help myself, but i go back to check if i didn't leave anything, if I am in a rush or need to get somewhere fast and can't go back, I start to not be able to breath and get really hot, and can't concentrate until I go back and check.