Hip arthritis almost always creates pain in the groin. If you do not have groin pain, but have pain in the buttock or the side of the hip, the cause of your pain is almost always due to a herniated disc irritating a nerve or the hole where the nerve leaves the spine is narrowed and, therefore, pinching the nerve.
Pain in the groin can still come from your back. Almost all of the lumbar nerves that come from your back can create groin pain.
Pain in the buttock or side of the hip is almost always due to one of the lower lumbar nerves. You should also know that the word “sciatica” just means pain down the leg and it could be coming from the L4, L5, or S1 nerves.