Ummm, worried about a lump!!!?

Hi all, iam a new member Madhu, and i'd rather not be venting my problems, right away, but i was just curious... just to have an idea, before i consult a doctor.
I have a lump under my left breast, it seems to have grown quite a bit recently, it's painful when i press it, to see if it's mobile/movable. I remember feeling something the size of a pebble long back, now it's definitely a big pebble! Iam worried about what the doctor will say. If there's someone, who understands what iam talking about, please let me know.

 

Hi Radha and Priya,
Did go see a gyn, at a hospital.
Upon inspection, she said that i had a sebaceous cyst under my breast, which was possibly infected recently, hence the soreness and the swelling, but no puss till now.(No MRIs or Ultrasound to confirm, she says she's sure!)
But she straight away declared that i needed a excision biopsy, when i asked if there was any other option, she put me on antibiotics for a period of 5 days starting today. Depending on whether there's improvement, she said we can go for the biopsy! I really don't want a biopsy as iam sure it's not benign. But i dunno if i am allowed to have mammograms to confirm, since iam only 26.
What do you think??