The hard lump in the cat’s belly after giving birth is not the uterus. It may be caused by hernia, tumor, or excess milk. You can squeeze the cat’s nipples. If there is a lot of milk, squeeze out some appropriately to avoid causing mastitis; if there is not much milk, It may be caused by hernia or tumor. It is best to take the cat to the pet hospital for examination to confirm the cause and treat it in time to avoid delaying the condition.