Why is my baby always constipated

So

My almost ten month old ebf baby is always constipated. He only gets fed fruits and veggies and none of the constipating type like bananas potatoes or whatever. Just leafy greens broccoli apples pears etc. but he’s constantly constipated. He pushes so hard and only a small pellet comes out. Sometimes nothing. He gets maybe one decent poop every three days.

And he gets looots of exercise.

Advice plz