Is he vaccinated? When did you last worm him? Worms can cause coughing & retching. He's moulting now because it's spring so are you combing him daily?As a long hair he needs your help to maintain a knot free coat & at 6 months old he will be getting a full thick adult coat, considerably thicker than his kitten coat. You can also add a teaspoon (5ml) of oil to his diet daily or feed a specially formulated longhair diet to help prevent furballs or fur blocked guts. Does he have a discharge from his eyes or nose? Can he run round playing without getting puffed out prematurely? or has he become more lethargic than normal? Is he an indoor cat or does he have access to outside? Lethargy, discharges & getting tired more easily need a vets investigation. He could be allergic to pollen or housedust mite pooh! Exposure to both can be managed more easily than you might think. Wheezing is usually only a problem if you can hear it normally - like accross a quiet room - not just when you have your head pressed to his side! If he has a persian type face he may just be a noisy breather. Even moggies can snore! Hope some of this helps & good luck.