High calories foods that help with constipation

My baby is not following her growth curve very well. The doctor told us to focus on high calorie, protein heavy foods. She’s been getting a lot of Greek yogurt, chia seeds, and peanut butter. I do give water with her solid meals, and sometimes prune and apple juice gets mixed in to her food as well. The poor thing is soo constipated though, and she cries and struggles every time she is passing a stool. Any ideas on high calorie foods I can feed her to help her gain more weight while also not backing her up so badly?