I was diagnosed with pneumonia 3 wks ago. Tightness in my chest has not gotten better. Xray, ct scan, vitals and EKG all looked good. What could be wrong?

Takes time. It's understandable that you are impatiently waiting to get well but healing takes time. Has your cough improved? Do you have fever? Is your sputum lighter and less? If the answer is yes, you're slowly getting better. O/W, ask your doc for reevaluation.