Desperate need of advice: 9 month old constipated

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I cannot seem to be able to cure my nine months old constipation.

He has lactolose at least three times a week and we’ve had to use suppositories a few times a week too.

He eats fruits, vegetables and we give him apple juice because that’s meant to help.

He does go to the toilet eventually but it’s big and firm and he’s in discomfort.

He’s formula fed but I still breastfeed my other son regularly, so I could pump if anyone thinks that could be the issue?

Please any recommendations needed!!!