HELP! Constipated 9 months SOLIDS and FORMULA

We are using Kendamil as babe formula. It was good for the first couple months until we start solid. I heard it’s normal but he was so constipated I gave him fruit prune juice and he release. But I’m afraid that prune juice will always be given to babe and I’m afraid of that will ruin his teeth. Fruit juices is known to give cavities specially for babies.

I feed him high fiber food and only twice a day meal. I did stop feeding him solid for the last two days as he just don’t go.

How many times a 9 month old should poop if they eat twice a day? My babe is once or twice a week.

He does not wanna drink much water even if I offer during and between meals. And if I give him water from bottle, he does not like to drink his regular amount of formula for the next feed.

So confused and desperate. Please help.