Hello. I am sorry about your difficulties. What come to mind first is the possibility that your stool has become harder, due to your recent dietary changes. By restricting carbs, you may inadvertently have dramatically reduced your fiber intake. One solution is to eat plenty of fresh leafy greens, which are relatively high in fiber, but low in sugars and calories. Make sure you are drinking plenty of water. Not doing so can also harden your stool, making defecation painful. You may also want to consider using a stool softener, such as docusate sodium. These are thought to be safe and harmless (as opposed to some laxatives). Another option is to gradually begin using a fiber supplement, such as psillium (Metamucil). Start with a low dose, and gradually increase over the next few weeks; if you start with too high a dosage, you may experience bloating. Again, be sure to drink plenty of water. It is possible you sustained a small tear, or fissure, around your anus, due to hard stool and straining. These typically heal on their own. Prostate problems can indeed cause rectal pain...but this is a bit unlikely given the scenario you present. Hope this helps, and best of luck.... get well soon! ez