how can I know if my newborn has reflux?

mother of 2 💖💙
Hello ladies,my baby will have 1month on the 8th & lately I notice that everytime he drinks milk and finished, he looks uncomfortable. He doesn't cry or vomit but he make sounds like something is bothering him. Sometimes he can't sleep cuz maybe his stomach hurt. I don't know, he burps after he finishes drink milk. He has an appointment on Friday but will like to know if anyone has the same issue with their baby & if what my baby has could be reflux? Thanks