I've been having a hard time taking a deep breath for the last 8 months. I can manage normal, short breaths, but I constantly feel the need to take a deep breath, and when I do, it just doesn't feel right. There's no fever, cough, or wheezing, but sometimes when I do cough, a tiny bit of clear, colorless mucus comes out. My X-ray came back normal, but I'm worried it might be COPD. I've never smoked, but I have been around secondhand smoke now and then. I'm still able to skip rope for about 4 minutes without stopping, and my SpO2 levels average around 98. Could you help me understand what's going on?