Poop troubles

Hi mummies. Need some advice regarding my baby. My baby is 9 months now. since newborn, he is not the kind of baby who will poop everyday. He will usually poop arnd 2-3 days bt they have been times when he pooped once every 5-7 days before he started on solids. Now that hes on solids, it is still the same but better maybe once every 2-3 days. But his poop is usually hard and almost blackish. He will usually go a bit red when pooping like its hard for him to poop. And sometimes, he will go red but there is no poop. We do give him probiotics, fruits,massage his tummy and lots of water and milk. Im at my wits end on what to do to help him. Most times his stomach is not bloated and he seems happy and doesnt cry when hes pooping. We’ve visited diff drs before and their reply is always to give fruits, water which we have been doing but its still the same. Im worried if it can affect him in the long run. Any tips or advices on what else i can do for him? Appreciate on the advices!