sounds like you are pushing too hard/slowly...try to use a dart throwing motion- it should only take a fraction of a second and no further pressing should be necessary- just aspirate and go...hope that helps
for me i use a 23g 1.5 for glutes. i dont do the whole dart it in thing. i do a slow controlled, firm, pressing of the needle into the skin and muscle and dont have problems.
i found if i hit a really bad pain spot going in i back off a bit a ever so slightly angle it just a bit and i dont have problems.
prob not related but when i used to dart it in and punch through a pain spot id get a bad bleeder or a bad cough.. maybe it was just me though.