Your breasts growing larger over months while you're losing weight usually points to a hormonal shift, not a structural problem. A fluctuating estrogen level can cause this even with a regular cycle. The nipple pain you're feeling often goes along with it.
Next Steps
A clinical breast exam is the right first step. Please discuss this with your gynaecologist, who can decide if a breast ultrasound or hormone test is needed next.
Health Tips
See a doctor sooner if you notice a new lump, skin change, or nipple discharge. Those need prompt evaluation.