When I first started doing my own shots I had a similar experience, i was doing it too low on my butt, which at the time still seemed like the upper outer quadrant to me, but you need to make sure you’re above the top of the bit crack and outside kinda toward your hip more. I had increasing heat and pain for a week which peaked at day 5-6 where I could barely sit down on that side and certainly couldn’t do any leg routine that week, it even hurt to lay flat for bench press, but after a week about it just went away and since watching some videos on exactly where to do the shot i haven’t had a problem ever since. Make sure you are using new needles every time and alcohol prep pads on both the injection site and top of vile to avoid any chance of infection. Don’t stress out