My partner is in alot of pain with a cough! HELP!?

My partner has had a very irritating cough for the past 3 weeks. He's constantly getting up in the middle of the night and is that bad he's sick with it. He's constantly gasping for air and he feels like his throat is closing up as he's coughing. The phlegm he's coughing up is usually green and it turns brown too. He's been in so much pain, the doctors said it was nothing but it isn't going away. We don't think its Asthma, but it could be whooping cough due to the noise he makes when he's coughing and gasping for air. he doesnt drink, smoke and is very healthy! Help!