i'm 26 yrs old and for the past few months, i've had a painful ,rather large lump in my right breast. it's located on the outside, upper part of the right breast--like at a 10 o'clock position, i guess. it is very tender and painful starting about a week or so before my period and lasting about 1 1/2 to 2 weeks---then the lump and pain go away for a while. what is this?? i have a grandmother and great aunt who have had breast cancer, but in their 60's. is this cancer?????