Ai, normal je lah, at 7 months when they start solids, their tummy is still adjusting to the change from milk, so the bowel movements get more active after eating! A few of my mum friends went through the same thing, and their babies' systems settled down after a couple of weeks. Just make sure the bubur is smooth enough and not too thick, and that he's getting enough water between feeds. If the poop looks healthy (not too watery or too hard) and he seems happy, you're probably doing fine, it's just his digestive system doing its job!