If the lump is mainly in the breast tissue and not under the areola or nipple then you can wait to see if it goes away after your next menses starts. If it doesn't, have it looked at by doctor. If it involves the nipple or areola or if there is any redness or heat (i.e. signs of infection) you need to see your doctor right away.
Almost all Ob-Gyn offices I know will work a woman in within a day or two for any breast mass or problem. It's a quick exam and the consequences of infection or possible cancer are serious enough to get anyone's attention. If it turns out to be something simple, that is ok; it happens often and no one is felt to be overreacting to want to be seen immediately.
http://www.wdxcyber.com/mbrpain.htm#m03
Hope that helps,
Kerry
Kerry, RN
Please click the accept button if this has helped you. A bonus is always appreciated as well.