What Causes Shortness Of Breath And Pain In Lower Leg After An Injury?

I am having shortness of breath after 2 flights of stairs and pain in my lower legs. Just a few months ago, I was able to go three flights with slight pain. I know I am out of shape but this seems different. I have high blood pressure controlled by medication. I also have RA and back problems. Walking a mile steady does not shorten my breath. m