My 11 month old hates to poop

I'm having a hard time keeping her regular. She poops every 3-4 days but whenever she feels the urge, clenches to hold it in. Not chalky like constipation descriptions say, but they are a bit firm. She's breastfed but also eats different foods throughout the day. I give her plenty of fruit (prunes included) and veggies, and avoid banana and rice. Any toast is whole grain. I've upped her water intake and stopped giving her the Gerber graduate fruit drops. Not seeing an improvement as quickly as I was hoping, and am looking for advice. I do plan on buying flax oil tomorrow to add to her food, so any experience on that are welcome as well.

Edit: Thank you all for the responses. I started her on ground flax mixed in her yogurt, and more juice.

I don't know why someone downvoted every comment in this post. I wish they had just contributed. Such is life.