Welcome to HealthcareMagic forum.
I would surely ask you to go in for an examination to your general physician or any doctor, to find out what it is, I feel it must be an abscess
of breast or any infection/inflammation called mastitis
, it could also be a significant swelling, like fibroadenomas/ benign tumors as well , better to get it examined
Avoid repeated trauma or friction to the area, wear loose bra which can allow a finger's width at least of space in between .