As someone whose dealt with a child whose had constipation issues and more recently an obstruction, unfortunately we were blind sided.
When DS was a baby, there were times when he'd have really loose stools, but his eating would decrease and his tummy would get hard and distended. We were told he was constipated -- lots of stool in the colon and instructed to try milk of magnesia to get him cleaned out. And after a day or so, he's usually have some fairly larger, harder stools that sometimes looked like they were encased in mucus.
When DS switched to whole milk we had issues with dry, larger hard stools.
And then he was fine, I'd thrown out milk of mag a couple years ago after we stopped using it.
More recently, DS had a bowel obstruction, but it didn't follow the usual norm for meconium equivilant. He got sick one night and the next morning woke me up 'cuz he had to poop. Threw up off and on and we assumed it was a stomach bug. The next morning, I picked up some milk of mag thinking he was constipate, obstructed, but he threw that up and later that night we took him to the ER 'cuz he hadn't stooled since the morning before and was in pain. Xrays showed his colon and the lower half of his small intestine were EMPTY, so it wasn't a normal blockage. Turned out in his case he had issues with surgical scars/adhesions that kept food, enzymes etc. from proceeding.