I had breast cancer 17 years ago. had radiation treatment, no chemo; lymph nodes were not affected. now have hard lump 2-3" in breast, afraid its bac?

There is no: way to determine what it is without an evaluation. Call your doc, you will likely need a mammogram and ultrasound for the initial imaging evaluation. You have a personal history of breast cancer so you are at increased risk, but even if you weren't, any new mass needs to be evaluated.

Possibly: This requires immediate attention. Have it evaluated now.