Breast ultrasounds- change in BIRADS

[Ina522]

Hi,
I'm 25 years old, and last week I did a breast ultrasound because of the fibreous "lumps' in my left breast.  THe radiology report read:"UPPER LEFT BREAST HYPOECHOIC MASS, WHICH HAS TEH APPEARANCE OF A BENIGN FIBROADENOMA.  BI-RADS CATEGORY3".
In April of 2007, I had an ultrasound done at a different location, and the result of the same breast in question read: NEGATIVE, BIRAD 1".
There is no history of breast cancer in my family, however, this change in "birads" makes me feel uneasy.  I don't feel that the grouping of this fibreous nodes has gotten any bigger, but I don't know what to make of this latest ultrasound reading. Also, the day I had my ultrasound last week was a day before I got my period- did that maybe influence the ultrasound interpretation? Should I be worried about this?  This latest ultrasound says that the "parenchyma is 9 cm from the nipple, and a homogenous hypoechoic mass, measuring 4.3 cm x1.1 cm x 2.5 cm and consistent with fibroadenoma".  
What should I do?
Thank you all!

[Ina522]

Thank you so much for your help. It just freaks me out that in one ultrasound in 2007 there is no mention of any measurements ( no centimeters provided of the "mass" and Birad 1), and then this year, there are measurements and a birad 3.  So, would you suggest a biopsy from your experience?
Thank you so much.