What Causes Loud Snoring And White Foam On Lips While Sleeping?

My 2 yr old son came down with Croup in Nov 2013. Since then he has been on antibiotics for ear infection and respiratory issue/congestion. He used to sleep soundly through the night, of which he doesn t anymore. He snores loudly and has white foam on his lips. Our pediatrician has sated croup goes away on its own, but I ve seen cases of chronic. Not sure if this has developed into asthma or allergy?