Diagnostic Mammogram tomorrow

Hi folks. For starters, I'm 44 years old.

On Dec. 23, I noticed pain in my right breast, the entire breast. Upon examination, I found what I thought was thickening at the bottom left of the breast and sharp pain there. So I called my primary care doctor, who referred me to my GYN (without even seeing me). My GYN did an exam and she said she didn't feel anything and had me schedule a diagnostic mammogram which is scheduled for tomorrow (Jan. 24). This morning I notice a small lump, maybe the size of a pea, on top of where I noticed the thickening. The pain is still something awful.

My mammogram is tomorrow and I'm not sure what to expect. I have a followup with a breast clinic next Wednesday (if I can get the referral squared away!). I keep telling myself it's just a cyst, but there's still the back of my brain that's afraid it's not. No idea what the diagnostic lab's policy on test results are. I know I'm going to have to bring disks to the referral (they asked for them).

I'm not sure what to expect anymore.

EDIT: I just learned that my older sister had breast cancer. We have had very little contact, and she couldn't (wouldn't?) Tell me what kind.