If you hit a nerve you would feel an immediate sharp shocking kinda pain and know not to keep going. It's likely you're just having a weird reaction to the specific spot you pinned since when you consider how small the needles are it is possible to stab thousands of different spots on your ass cheek and we never nail the EXACT same one each time. Not all of our meat is created equal, some spots are fine and a millimeter away you can stab a shitty spot. Just try to mentally note the general area and avoid it by 1-2cm for a bit if you have the surface area for that. Probably use the other cheek for a few shots too. If you are genuinely worried just go to a doctor and tell them you do your own HRT and are worried you fucked something up, no other details needed other than "I do my own HRT". They do not need to see scripts or anything for this, you will not get in trouble.