I left him some food and water before I left for school and when I got here he drank water only but when I got home my room smelled like poop and there was poop stains but I didn't see any poop. Well after he drank water and peed I picked him up to my bed and he just suddenly threw up some brown liquid with some of his dog food and stinked bad!! He's 9 weeks old and a boxer breed. After he puked he ate all his food I have him and pooped like 5 mins after. Why did he throw up?