I Am 57 Female And Fairly Active The Past Month

I am 57 female and fairly active the past month I can't even walk up a flight of stairs without resting any exertion exhausts me I am a teamster by trade an am used to hard work the simplistic tasks I née to rest just walking to my car I have to stop 2 or 3 times and I usually walk 6-15 miles everyday I work I did go to a dr that did an ekg and vitals vitals ok ekg was not normal but nothing to worry about gave me inhaler no improvement