Having Constant Mushy Poop Between Butt Cheeks. Has Painful Diaper Rash. Suggestions?

My daughter is 4 years old and is having a constant mushy poop that will be stuck between the butt cheeks or just hanging onto the butt. She sits on the potty when she starts to try to poop, sometimes she initiates, sometimes I do. Because she tightens and squeezes her butt cheeks together when I wipe her to make sure all the poop is out of her butt, I can't. This has put a damper on our potty training, switching from pull ups to panties. She also today has now got a very painful diaper rash & has broken the skin. I am using desitin for the rash. My main concern is why isn't this poop stopping or why isn't it a solid poop and then be done with it. Prior to this back in May, she was nearly impacted and we had to give her a stool softener in the rectum. It was relieved in minutes. She seemed like she was back on track. Then about a month or so ago, she was pooping only every 3 days, sometimes I think holding it in? What to do, what to do.....