Every kid's different. My sister had the same and I think it also was a issue with constipation. She actually was on medicine to help with that and that was the only way she was ever able to get potty trained. Have you tried incorporating foods that act as natural laxatives?
I'm not sure if you're planning on having any more kids but we're doing elimination communication with DD and that's been going really well. We did it primarily because we didn't want to go through the same thing my mom went through with my sister and also we got sick of DD screaming through her diaper changes.
