if it still hurts it can usually be the gear ur injecting, not where ur injecting
e.g i inject test cypionate, a UG lab my friend homebrews, i can inject it in my ass, quad, tricep, lats and even biceps, and the next day it is painfree like ive never even injected anything
rather if i inject test prop, whether it be arse, arms, or shoulders i can barely move that muscle for days