I have a mole under my breast. What kind of doctor do I go to see?

You should please see a board certified dermatologist for this issue.  First, they will confirm the diagnosis (many times people come in thinking they have a mole but it is something else) and then assuming it is one, you would want it to be surgically removed by the dermatologist and have the specimen read by a dermatopathologist (someone who looks at skin samples under the microscope to make certain they are healthy).  The mole may be removed by either shave excision (no stitches) or punch excision (with stitches)--each option has its benefits and potential drawbacks.  Take a look at the American Academy of Dermatology website for a board certified dermatologist near you. 

Dermatologists are the experts in skin diseases so I recommend you see a board certified dermatologist. If it needs to be biopsied or removed, typically a shave
excision is the easiest, most cost effective, and least likely to
scar method of removal for that area. With this method the mole is actually
"shaved off" at a level just below the surface of the skin. The
tissue that has been removed can then be sent for microscopic examination to
make sure the mole is benign. Dermatologic
surgeons are experts at doing this procedure.