I Bite my nails intill they bleed because i stress out all the time help.?

I need help i been biteing my nails intill i was 8 years old and had never stoped because i lived a stressfull life. i have post dramtic stress sisorder and it killes me i cant talk to anyone, im not social, and just sad. my nails bleed wheni bite them and they hurt like hell but i still do it i alwqays stress and think i will fail all the time. i hate having post dramtic stress i wnat it gone and want to live and normal life im 18 and i stress about everything what to i do.