you can still be constipated even if you poo regularly. Really, it's true. Is your poop hard and sometimes in small bits or massively huge? Both are signs of your digestive system and intestines moving slowly. I'd try seeing if you add some fiber to your diet, eat more fruit, try some foods that cause a laxative effect (cabbage? grape juice?) and see if it helps. If the pain gets worse, see your doctor. This isn't like muscle strain or spinal stenosis, slipped disc, nerve impingement though, is it? Is it relieved by stretching? Does ibuprofen help?