Congested Shih Tzu, please help him!?

I have a 8 week old shih tzu pup, he's a hyper 1.7lbs. He sleeps alot, eats and drinks good, urinates normal and his poop hasnt changed. But he now sounds congested. Sounds like hes got some snot trapped back there! Sometimes he has to open his mouth to catch his breath! He has an occasional sneeze every so often a cute little cough. I hear dogs dont get colds, but I also hear allergies in the shih tzu breed is normal, with his little nose it seems so tuff to breath sumtimes. The vet put him on 1/8 the temaril tablet cortisone/antihistamene....been four days, doesnt seem to be any better. does any one have this problem with their tiny nose breed dog? If so how do you help it? I am afraid to do benedryl, and the saline drops freak him out! HELLPPP!