I am at my wits end trying to potty train my 3 year old. He will never tell me that he has to go so I go by time, putting him on the potty every 1-2 hours. Sometimes he will go pee, but he almost never will go poop. He will go hide in his room and poop in his pants, underwear, or pullup (any type of bottom that is on) after holding it in for days. And just when we have a few days of no peeing accidents and I put him in underwear, he decides to pee his pants. I have done a potty chart, mnm prizes, a small toy… nothing seems to make a difference. I am so sick of spraying poo out of clothing when I know that he is smart enough to know he is supposed to go on the potty. He always says next time he will poop on the pot. I honestly don’t know what else to try 
What worked for you?
My 3 year old was the same way. I tried a kid potty, a cushioned seat on the big potty- everything. I did the same as you putting her on throughout the day. Having her drink water and (honestly) bribing her with a little juice so she’d go pee. Peeing was easier. But pooping nearly impossible. She’d hold it in until she would wake up in the middle of the night crying from stomach pain. I eventually let her bring her tablet with her to watch Netflix while she sat on the potty waiting to go. I’d rub her back and try to make it as peaceful and non-scary as possible. Eventually she went poop more and more. Once she got over the fear. It takes time but hang in there! He will let you know when he’s ready. I know it’s frustrating and tiring. I was under some preconceived notion that she HAD to be potty trained by a certain time. But honestly it’s all in their timing (within reason lol). Try the iPad or phone. If he gets relaxed enough, he will go.