How often should I put Karo Syrup in my babies bottle? He has only pooped once in a week, and it was…

How often should I put Karo Syrup in my babies bottle? He has only pooped once in a week, and it was super thick and he hasn't pooped since and his belly is hard as a rock. I've been doing warm baths, thermometer in the butt, apple juice, just EVERYTHING and his belly is still hard as a rock 😖. But I ain't used Karo Syrup since my daughter was a baby so I don't really know how often I should put it in his bottle!