Hey mamas. I need some help. Robby is. I guess constipated. He is still pooping. But it’s little…

Hey mamas. I need some help. Robby is. I guess constipated. He is still pooping. But it’s little balls. And there’s some strain when he’s going. What could be causing this? I half breast feed half formula. He’s getting the same formula he’s been getting. He’s had solid food for almost 2 months. Hasn’t really changed what he has been getting. Maybe the amount is more. WhT could cause this. Is he getting too much food. Not enough. What can I do to alter and help