What Causes A Pimple Like Bump Under The Nipple?

hi, i woke up this morning and noticed something that looked like a pimple just under my nipple. I havent tried to squeeze it but I have been putting warm water on it to try to draw out the fluid. Could this be something serious or should I just keep doing what Im doing and hope it goes away? Breast cancer doesnt run in my family. What could be the cause of this?