Bm help

My son is 8 months old. At 6 months old he was put on zantac and it made him constipated and then he was have a hard bowel movement. I stopped giving it to him and he started having soft bowel movements and then he stopped pooping for a few days and then had another hard one Sunday. He had a soft one today after I’ve been giving him prune juice and baby food prunes. He screams when he had the soft bm just like he did with the hard one. I’m going to call the doctor tomorrow, but I just need some advice or tips for now