you put a hole in your muscle and then injected oil.. so your muscle is pissed lol.
make sure you keep the needle stable and injecting slow can help.
i recommend you hit your delts next. then move to your quads. those are the easiest ones. and then the pec is an easy spot once you get the hang of it.
for real? i think pec is way easier than delts...two hands are better than 1
also, OP - some people buy their syringes with 20 or 21g to make drawing faster, and then change the pin (which you should be doing anyway) to a higher gauge for injection