yeah, i tried meth for the first time recently and scratched the fuck out of my neck for no reason. personally i found that it helped to tie my hair up, i stopped messing with my hair/neck as much after that. i heard prenatal supplements can help with hair growth and can improve skin and nails, so maybe try that. there are other good vitamins too. take supplements and eat healthy and youll be fine.
if you have issues with picking at your skin, keep your nails very short. the soaps and shampoos you use matter too. use gentle ones, ideally ones for dry/damaged skin/hair. remember to stay hydrated as well, inside and out. apply lotion after you tweak and drink a lot of water.