I would make another apt, perhaps if there is a different GP in your surgery, and insist on a referral to a breast clinic as any changes to the breast should be checked out, they are the experts, regardless of what your age. It does not mean that it is cancer as they deal with lots of other breast conditions, for example cysts which they can drain.
I'm 23 years old and have had a burning sensation in my breast for the past 2 months. It starts from my chest wall and radiates to my nipple, this happens up to 10 times a day. One of my Montgomery glands on my nipple also pusses every day. Anyone else experienced this? The nurse at the gp put me on naproxen and examined me. When seeing the gp he wasn't interested - said I was too young to have any form of breast cancer (which is not what I'm 100% concerned about!)