This is an interesting question, and hopefully we can help direct you to get the information that you need. An ENT (ear nose and throat surgeon
, aka otolaryngology-head and neck surgeon) may be a good place to start. There are many possible explanations for the symptoms that you are describing. Swelling and pain under the jaws can be due to dental infections, as you already have suggested. Although having healthy teeth is usually an indication that this is less likely, there are some occasions where people will have odontogenic infections despite having what they thought were healthy teeth. Other possibilities include common infections and colds of the upper respiratory tract, which can all lead to swollen lymph nodes. This can be tender in some cases, and can lead to some increased volume in the nodes as they swell to help fight the infection. There are other things as well, some of which are more dangerous and can have long term effects if not treated in a timely fashion. Depending on your past medical history, these may or may not be more likely. The key thing is that you will need to discuss this problem with your doctor
so that you can get the help you need. Again, an ear nose and throat surgeon, may be a good place to start.