15 months baby doesn’t eat and poop yellow/beige

Hi everyone. I want some ideas please if not I’m gonna Lois my mind. My 15 months old son it has been 2 weeks that doesn’t eat nothing at all only milk milk milk. Some yogurt maybe a little bit of cheese. And his poop is yellow very light like beige. We took him to doctor and they ask for sample to see if any bacteria or parasite is present. I’m waiting for their answer. Anyone has a similar situation? How to make my baby eat? Before he used to eat a lot a lot. Maybe teething or I don’t know. But no fever no yellow skin..he is very good hydrated but still don’t know. I’m very worried