Betty, from what you describe as the location of the sore area, it may be lower than a lymph gland normally is. Check this diagram of the lymph nodes in the body and see what you think:
If you think it might be one, here is the Mayo Clinic's page on swollen lymph nodes, including information on when to seek medical advice:
Here is some information on breast pain, and things that can cause it:
If the pain doesn't go away, it's a good idea to check with your doctor; no concern is too small when you're protecting your health. Let us know what you find out.