I had a similar experience. Just a couple of weeks after my AVR, I felt like I had caught a flu bug but was fighting it off. I had cough and congestion, felt really fatigued, and just felt like I had the flu. What I didn't realize was the obvious. I was in congestive heart failure (CHF). The water had gone from the area around my heart into my lungs. Thus the coughing. It started out small on a Monday and sort of waxed and waned. But by Saturday I figured I had better go to the urgent care as Friday night was the worst. I was up all night coughing and being very productive, getting lots out of my chest. I thought for sure it was a chest cold.
I ended up in the hospital for 5 additional days. I also had a-fib and a-flutter. They waited a couple of days for me to respond to the meds before deciding to give me the shock and that worked like a charm. I instantly felt better!
Most people probably just have a cold, but it's definitely something to have checked with your doctor. Make sure you rule out the possibility of chf together.