what can i do to help my seven month old get rid of snot in in his lungs?

My seven month son has health issues so i dont know what all i can do. He has a g tube because when he drinks it goes into his lungs as well as his tummy. He does eat some teething cookies and seems to do fine but the last week he has a real bad cough when laying down and sounds bad when breathing. Not all the time though. No fever no puss or anything. He does cough up snot sometimes. What all can i do to help him?