It makes sense to be aware of your breasts and know what is normal for you. Each breast contains 15-20 groups of glands designed to produce milk. Channels from each gland join together (a bit like a bunch of grapes) and each cluster has a main duct which opens at the nipple. The glands are embedded in fatty tissue which gives the breasts their individual shape.
By regularly checking your breasts you become aware of what is normal for you throughout the month. Familiar lumps and bumps that do not change over the months are not a cause for concern. If in doubt about any particular area of your breast, feel the other breast and if the lumpiness is the same on both sides, all you need do is check them again the following months.
If you are still having periods, do this a few days after your period, if not, make it the first week of the month. Many women have breasts which are slightly different in size. If your breasts have always been like this there is no need to worry. However, if there is a change in the shape or size of one of your breasts, consult your doctor.