Your symptoms are very similar to mine. I am a healthy, fitness addict, 40-yr old. 4 Weeks ago felt shortness of breath during my workouts, "broken" ribs pain, and violent coughing when working out. Otherwise, felt fine. No fatigue, no other real major symptoms. Doc listened to lungs and visual inspection of throat, nothing. Went and got x-rays and discovered 2/3 of left lung with pneumonia. Wasn't sure whether it was walking version, but was prescribed 875mg/125mg Amoxicillin.