What kinds of infection cause swelling of the lingual frenulum?

Sialolith. You frenum is a small band of elastic connective tissue that connects your tongue to the floor of your mouth. It hardly ever gets infected. You probably have a little calcified stone called a sialolith blocking one of the salivary ducts around the frenum and causing swelling on the floor of your mouth and frenum. See your dentist asap!
Not many. The lingual frenum is a small band anchoring your tongue to the floor of your mouth. Rarely will it get infected i would bet it is the 2 salivary glands on either side of your frenum. See your dentist.
See a Dentist. The best way to resolve swelling is to see a dentist to resolve it if it is an infection and to rule out something more serious. A velscope pre-oral cancer screening would be a good idea.