I'm a twenty years old with a family history of breast cancer. i noticed a lump that has grown over the past few months. should i be concerned?

Unlikely: It is unlikely at the age of 20 that it would be breast cancer. However, if you are concerned and have a family history, you should have an exam performed by your primary care provider.

Have it checked: At your age, it is unlikely to be breast cancer, rather it is probably a benign lesion. Pending on the age your family members were diagnosed with breast cancer can have a bearing on whether or not you should be concerned. With your family history of breast cancer, it wouldn't hurt to have it checked out.

Obvious: I think the fact that you asked the question shows that you are concerned, and with some reason. Although it is rare for someone your age to have breast cancer, it can happen--particularly in women with a strong family history, or known carriers of the breast cancer genes brca1 or brca2. Please see your doctor who can better assess your risk.