Coughed up something strange, what is it?

So the other day i coughed up something wierd. It was a membrane covered sac that had yellow goo in the middle that smelled awful,= and reminded me of feces. The outside was clear.. It was roughly the size of a marble and it was in the shape of a kidney bean. Help me figure out what this is! Thanks Reddit <3 TL;DR coughed up yellow sac. what is it?