I have a hard mass/lump under my left breast right where the cup of my bra sits. it makes me think it is a callous. it hurts if i push too hard on it.

Skin lump: It is possible you sustained a tissue injury - mild - breast tissue is sensitive to "fat necrosis" actions - where healthy adipose cells break down - and take the form of a bruise - that can then scar internally and even pucker or produce a lump. To be optimally careful, an expert exam can assure you - perhaps an ultrasound is needed; it is highly unlikely you have developed a tumor there

Worth checking: You should have it checked by your Primary care. It may be a rib cartilage that is causing you pain, or it may be something in the breast itself. Callous is unlikely. Thanks for trusting HealthTap!