VETSCOPE

My dog has always had symptoms of coughing up phlegm every now and then, but from last night it's gotten worse. It's more frequent, sounds like coughing, and he looks like he's struggling to get it out. Every time we go to the vet we've been asking about the phlegm, but they wouldn't really look into it. We also told them about a runny nose, and they gave us medicine for allergy. Considering the time of year I guess it might be hay fever or a cold, but I'm a little concerned because of his age. Everything else about the dog seems normal. Do dogs generally cough when they catch a cold?