Aww don't worry, yan normal lang at actually good sign, some babies at 7 weeks na talaga marunong mag-burp on their own, especially pag super full na sila from feeding! I'd still keep doing your 20-min upright position after feeds para peace of mind lang, pero kung nakita mo na consistently na siya mismo ang nag-burp, mas relaxed ka na pwede hehe. A few of us moms noticed na ang aming babies did this too around that age, sign na umuunlad na ang kanilang digestive system. Just watch out if baby seems uncomfortable or bloated between feeds, pero kung normal lang ang behavior niya otherwise, I think you're all good!