Not pregnant or on pill. noticed (one)consistently veiny breast and puffy nipple for months. no changes based on cycle. what is causing this?

Breast abnormal: Even though not on pill or pregnant, your breasts do change with your cycle (sometimes more tender and swollen before your periods, etc.) . On occasion, one breast may have more secretions than the other (breasts are rarely the same exact size) and extra veins can be seen in one and not the other. Ask your healthcare provider to examine your breasts and perhaps get a mammogram to be certain.

Asymmetry: Very few people have two identical breasts, so I believe the difference has to do with a slightly different vascular architecture, not necessarily a medical condition that requires treatment. If you are concerned about the appearance or are experiencing pain, by all means have your OB do a thorough breast exam and a possible follow-up ultrasound or mammogram to settle any worries.