Your body will adjust to the fascia stretching and the solvents within. If injecting 2 mls at once EW hurts, try splitting the shots into 2 seperate shots.
Things to keep in mind:
The amount of oil, the speed of the injection, the depth of the needle, the type of gear, the ratio of solvents and the virginity of the muscle all play a role in pip.
Your body will get use to it in time though.
P.s. i started in glutes.