In the fifth month of pregnancy, the pain in the left buttock is considered to be caused by the enlarged uterus pressing on the sciatic nerve. If the pain is serious, you can gently massage to promote blood circulation and improve the pain sensation. If there are symptoms of calcium deficiency, it will also cause pain in the buttocks, you need to take the right amount of calcium, you can eat calcium gluconate for pregnant women, and usually eat more food with high calcium content, such as boil some bone soup to drink, or eat more seafood, usually pay attention to more sunshine to promote the absorption of calcium.