I am 29 and thinking of getting my first mammogram because my sister recently found a cyst in her breasts. She was only 18 at the time. I was drinking 5 cups of coffee and got one too, but it went away a few days later after I cut back.
Cysts are not cancer, they can come and go very often and are harmless, they can be so small, and they can also grow quite large. If you want to be sure it is a cyst, then you could ask your doctor to send you for an ultrasound and that would show you what kind of cyst it is, simple cysts are most common. But if it puts your mind at ease, then I think you should ask your doctor what he thinks about you having a mammogram. He will ask you more about your family history to ascertain if there is justification to have a mammogram.