The pain in the buttocks after the injection is mainly due to two reasons: 1. If the pain in the buttocks occurs immediately after the injection, it is possible that some drugs, such as vitamins, have a certain stimulating effect on the muscles and cause pain when the local muscles are stimulated just after the injection, and the symptoms will generally be relieved after rest. 2. If the thighs are weak, consider that the sciatic nerve may be damaged, causing numbness in the lateral part of the calf or weakness in the legs when walking. You can give local hot compresses or physiotherapy, and the symptoms can generally be relieved after rest. So the buttock pain after the injection is mainly due to the above two reasons.