I don't know that you should be worried because there are many possible benign causes for these issues.  You can read some background information in our sharepost about armpit lumps.  Swollen lymph nodes usually means that your body is trying to fight off an infection, but sometimes they can be a sign of cancer.  The main issues to consider right now are how long you have been having these symptoms and how severe the burning is.  If you are in pain, you will want to contact your doctor soon.  If the burning is more of a discomfort issue, you could watch and see if it gets better or worse over the course of your menstrual cycle.  Knowing how the lumps and/or burning change can be useful information to your doctor in trying to diagnose the problem.  However, do not wait longer than a month before checking in with a doctor.  Breast changes that do not go away within a menstrual cycle need to be checked out by a doctor.  So don't worry, but do continue to monitor the situation and take action if the problem persists.