It may very well be an inflamed mammary gland, but you need to be sure. You need to INSIST on a fine needle biopsy and a mammogram. That is the first step. Yes, you are very young, but cancer does not know age. Believe me I had breast cancer 10 years ago and I was told I was too young. I also had a lump that was painful and was told, by the doctors believe it or not, that breast cancer is not painful.
Well, I took my health in my own hands and demanded that something be done. I went through 7 doctors before I found one who would actually listen to my concerns. And, yes, I did have cancer.
If you have a lump and can feel the lump, become proacitve in your own health and make them check it out. The first doctor I saw said that I had fibroids. So, I listened and waited. Three years later it was not a fibroid but breast cancer and I had to have a bilateral radical mastectomy. Had the original doctor done his job I could have had a simple lumpectomy.
So, please seek a second, third, or fourth opinion if you have to.