Can you have pneumonia for awhile and not even get seriously sick?

Sometimes. Pneumonia can range in severity from mild to quite severe. Just depends on your overall health and the type of infection you have. Pneumonia can be caused by bacteria, viruses, and fungi. Other disease processes like aspiration, COPD, asthma, interstitial pneumonitis have pneumonia like symptoms.
Yes. Atypical pneomonias can run an indolent course, in older pts 50%pts have no pulmonary symptoms like cough shortness of breath or fever, confusion could be the main symptom.