You could be pregnant, but there are many other things that can cause this too. You can have tender breasts from the first week of pregnancy. I don't know how old you are, but it could be from PMS, ovulation, changing your birth control pill, and other causes.

Make sure you are wearing a bra that fits you and provides support. If you need help getting the proper fit, you can easily find someone at the department store who will measure you for a proper fit.

I did some research for you and found a list of 76 causes of breast pain. You can look here http://www.wrongdiagnosis.com/symptoms/bre ast_pain/causes.htm

If your conditions worsen or persist, you should check with your doctor, but do check to make sure that you are also not pregnant.