Could swollen gland on left side of throat over a month be caused by anything other than the tooth infection on back left lower molar that was removed?

It is possible. Swollen glands are a sign that your body is fighting an infection or another type of illness. It could be caused by tooth infection, skin infection, ear infection, sexually transmitted disease, etc. See your PCP for evaluation and treatment if needed.
Yes. The cause of this swollen gland can be a number of things other than a tooth such as throat, sinus. It is important to get this diagnosed and treated. See a dentist, or oral surgeon ASAP.