If my six month old isn't eating as well as he usually does, isn't sleeping well, coughing, and wheezing, what could it be?

Bronchiolitis: Winter cold viruses in young children and infants travel into small breathing tubes and cause wheezing and chest congestion, esp in winter months. If breathing is labored, or cough spasms or wheezing are heavy then you should seek medical attention. If symptoms are mild then simply suction nose, if needed, and monitor for complications such as earache or fever. Usually lasts a week or so.

Bronchiolitis: The symptoms you described suggest he probably has bronchiolitis, an inflammation of fine branches of wind pipes. Have him checked.