If the concern is breast cancer you can watch it for a month and see if it tracks your cycle. But I would be concerned about a latent infection or blocked duct, so I would see a doctor.

I have the same issue and just had my annual exam today. As happened last year, my doc felt nothing but this time he did give me a referral for a baseline mammogram. I am two years out from breastfeeding and my right breast is very sore and tender when touched even lightly.

Costochondritis? Google it and see what you think.

please see your doctor, don't mess around

just so you know it could be a clogged duct; it took me almost two years for my milk to dry up completely

but please, please see your doctor

On and off for the past few weeks, I've had days where my right boob -- and only the right boob -- is sore. The other is a little tender, but nothing like the right one, which hurts when I touch it or even when I walk. I'm about a year out from breastfeeding, in the middle-lateish part of my cycle, and I don't think there's any way I could be pregnant. It happened last week but went away. Dr. Google says probably not cancer. What could it be? Please advice, Nurse DCUM.

ETA: I am 30 years old, if that makes any difference.