See your doctor. To answer your question properly requires a physical exam. It is not possible for me to tell what the lump is without an exam. Any breast lump is concerning and requires the proper history, physical exam, possibly an ultrasound or mammogram for complete evaluation.
Self-detected lump. An exam by a qualified physician is appropriate doesn't require expensive testing, should be affordable to evaluate without health insurance (as most outpatient conditions are, as well).