I m 43 and work out at least 4 days a week so I m pretty healthy and not overweight, non smoker, but for a week now I ve been having back pain on the left side close to my rib cage. It really bothers me when taking deep breaths. I assumed if it were a pulled muscle it would be a lot better by now but it s not at all. I ve also been short of breath but that s a symptom I ve had for a few years now. Went to doctors and it s just been anxiety. What could this be? I ve had kidney stones before and know for sure this isn t coming from my kidney because the pain is higher and mainly hurts when taking a deep breath.