Is it possible to have a tooth infection for a few years?

Sub-clinical: A subclinical infection can be present for a long time. It's a balance between the bacteria and your immune system in a confined space. If the infection starts to grown and causes a bigger immune response, you'll get plenty of pain and swelling... Take care of it now.

Of course: Many teeth that require root canal therapy are already infected for many years. See your dentist for consultation.