My son is Constipated

My son is 3 months old and hasn’t been pooping like he normally does. He’s breastfeed and always has pee in his diaper but lately he’s been getting tummy aches at night which is preventing him sleep I thought it was the medicine he’s on but I took him off of it and it wasn’t this is the second day now and he keeps bringing his legs up at night and whining and I feel helpless does anyone have any suggestions?