I have the same problem. When I was 30 years younger and fit, running 5 miles a day I was breathing hard too Years of sitting behind a desk, weight gain and getting back into running with c25k it seems worse. I run on the track at the Y where it is level, a little springy, and climate controlled helps a lot. I also find that distracting myself takes my mind off it. Listening to music, counting rhythms, just musing, I don’t notice the difficulty breathing as much, even though my pace doesn’t change. I am on week 8, just finished day 1, and I am 5 minutes in and feeling like I can’t make it. By minute 15 I am distracted and am contemplating running and extra 5 minutes. As soon as I focus, though, I start noticing the heavy breathing, and struggle at the end. Being distracted is probably not good for improving time, or if your out in a less controlled environment, but it gets me through my runs.