I had a very similar experience when prescribed Lipitor about 20 years ago. I was in my mid-forties running about 30 miles a week and doing other exercise as well. After about a week on the drug I started to experience exhaustion and could barely get around a 1/4 mile track once. I also gained about 15 lbs in the 3 weeks or so I was on the drug. Since the drug was obviously the cause I stopped it and within a month everything went back to normal except the weight which took a few months to lose.