How common is it for somebody to get swollen gums?

Swollen gums: The most common cause of swollen gums is poor dental hygiene (not brushing enough). In this case the gums also tend to bleed when brushed. Swollen gums is very unusual for a person with good dental hygiene. Other causes include allergies, drug reaction (particularly dilantin), leukemia, and other disease that can cause infiltration of tissues with cells or abnormal proteins.

Gums should: not be swollen unless caused by infection, allergic reaction or medication. See a dentist asap for proper diagnosis and treatments.