Persistent leg pain after a buttock injection may be due to local nerve irritation or muscle injury (sometimes called injection-related neuropathy), while discomfort in the kidney area may or may not be related and needs separate evaluation. Since this has lasted two months, the next best step is to see a neurologist or orthopaedic doctor for a focused examination; they may advise tests like a nerve conduction study or imaging if needed. Continue Methycobal (vitamin B12) only if it was prescribed for nerve symptoms, but creams like Dermanex are unlikely to help deep nerve or muscle pain. Gentle physiotherapy, stretching, and simple pain-relief medicines can be useful if advised by your doctor. For the flank/kidney discomfort, basic tests such as urine examination and an ultrasound can rule out kidney or urinary causes. Seek urgent care if you develop worsening weakness, numbness, difficulty walking, fever, or severe pain.