My 6 day old sounds stuffy and sometimes wheezing. Is this normal and should I use a humidifyer?

Yes and no. Some stuffiness or sneezing is normal in young babies because of their tiny nasal passages. But much wheezing or coughing, on the other hand, might be signs of something that should be addressed, such as a respiratory infection or reflux.
Not normal. Wheezing indicates difficulty breathing . Unless you are confusing the nasal / upper airway noisy breathing for wheezing .I would have the baby seen by the doctor.
YES. A humidifier is useful but you must be vigilant at cleaning the machine at least once per week. If your child is stuffy, consider a nasal wash, safe, inexpensive, effective when done correctly.
Clean the air. The first months are troubled by narrow nasal passages & exposure to dust, fragrances, smoke & other irritants.Baby tries to flush these out of the nose with mucus but this often ends as congestion & produces rattling with breathing. The best rx is washing out the nose with saline & suctioning the remainder.Eliminate irritants from babies environment & this will happen less.Humidifiers do little.