Jaime, 

This article on breast pain can help you evaluate whether you need to see a doctor right away for this particular problem.  If the pain is in both breasts, it is extremely unlikely to be cancer related, and off and on pain is also not usually a cancer symptom.  If the lump that was there when you were 17 is still there and is still the same size, it is not likely to be cancer.  However, if it has grown, then you definitely need to see the doctor as soon as possible.  Now that you are in your 30's, it is important that you start seeing a doctor regularly for your "well-woman physical" which would include a breast check, but probably not a mammogram until you are 40 unless the doctor finds a problem.  If you have a good income, but no health insurance, then you can save up to pay the doctor cash once a year for your check-up.  If the doctor finds a problem that would be expensive to treat, there should be assistance available to help you.  If your income is low, then you are probably eligible for free or reduced price clinics in your community.  Don't continue to live with this pain; although it probably is not cancer, it may be a symptom of another problem that needs attention and the doctor will probably have suggestions about how to relieve the pain.