I Am 54, I Started An Exercise Boot Camp 6

I am 54, I started an exercise boot camp 6 months ago. I started eating healthier and lost 35 lbs. I feel great. BUT recently, I have noticed that my stamina during workouts is hindered by a heavy chest feeling. I am under some stress at work and it is getting cooler outside where I work out, but I was wondering is this could be asmah (don't know spelling). I've never had it before, but it runs in the family?