Painless injection itself will not cause back pain, mainly related to the inflammatory reaction after painless injection, may also be caused by normal uterine contraction. 1. Inflammatory reaction: when the painless injection will cause some damage to the local skin, local inflammation may occur, thus causing back pain. If the back pain is mild, usually no treatment is needed, but the local area should be kept dry and clean in order to promote recovery. If the pain is severe, you can follow the doctor’s instructions oral amoxicillin capsules and other anti-inflammatory anti-infection drugs. 2. Uterine contractions: The uterus will contract irregularly after delivery, which is a sign of uterine recovery. Abdominal pain can occur during uterine contractions, usually accompanied by low back pain, which is a normal phenomenon, and is not very much related to the painlessness of the fight. This is normal and not related to the painless injection. Generally, no special treatment is needed and the symptoms will gradually disappear with time. It is recommended that if you experience any discomfort after the painless injection, you should seek medical attention in time to avoid any delay in treatment.