(Buried in kiwi's thread)...thought I'd start a new one for ya.
None of us here are doctors, but what I can tell you is that no one can tell what the lump is without really looking at it. That means ultrasound, mammography and possobly a biopsy. Try to relax though, 80% of breast lumps are benign. Primarily, people our age get cysts tht are fluid filled and can change with the time of month. Fribroadenomas are benign solid tumors, that sometimes are removed by surgery. While I am guessing that the tumor itself does not change with your cycle, the texture and density of your breast tissue may change, causing you to feel it differently.
The mammogram should be offered, but in my case, at age 30, the mammogram was not an effective tool. The ultrasound showed malignancy, but we are all different and one test may or may not show something in different people. They say "moveable" is a good sign, but in my case it meant nothing.
Do not let them dismiss you "because you are too young." I was 30 when diagnosed and we have had gals here diagnosed in their 20's.
Most likely this is nothing, but absolutely has to be checked out. Make sure you have sufficeint evidence, not just a nurse's opinion, that says it is nothing. Keep us posted...