Carol, JoAnn gives good advice. Also, keep in mind it can be just plain old nothing! The lump could be normal lumpy tissue, and a coincidence that there is ternderness there. 80% of breast lumps are benign, so the odds are in your favor.
And as JoAnn said, all of us had different experiences. My tumor was round and firm, felt like a walnut in oatmeal. It was distinct, but not particularly tender. 30 of us will probably report about 25 different scenarios, so there is no way to tell.
Chances are this is nothing to worry about...but please do not be satisfied if the doctor just tells you it is a cyst and to go home since you are low risk. Only 5% of breast cancers are the "inherited" type, and many of us here are in our 30's. The doctor cannot tell what it is without doing tests, and he should start with a mammogram and ultrasound.
Odds are in your favor.....but be your own best advocate!