Hello!! I am 32 and last year I found a knot behind my left nipple. With pain when touched. I went to the doctor and she set me up with a mammogram and ultrasound. Done both came back they couldn't find anything. Even thought my doctor found it and found another one below it. I have noticed that right before my period the knots get bigger and hurt really bad.... Then a week later it goes down but still painful. Its starting to hurt so bad my bra hurts to wear. Any ideas what it could be or what I should do.