What Causes Pain In Breasts?

Hello, Iam 27yr old female. I have pain in both my breasts for a week now, predominantly in left.I did a self examination and did not find any cysts or lumps. I went to a GP , she did a exam and prescribed me evion-LC 400mg for 15 days. My periods are not until another 10 days I just want to know if this is a cause for worry and if mammogram needs to be taken to rule out any cysts.Iam also on OVRAL-L for past 3 months. please let me know