18 month old son has a very flemy cough?

He woke up in the middle of the night choking and coughing. When he breathes, you can hear the flem. He fell asleep after an hour of playing to keep his mind off of it. This morning he is the same but its worse when he first wakes up. I think he might have a bit of a sore throat also. Do you think it's bronchitis? What should we do?