Hi, I Have Started Taking Ginette 35, The 21 Days

Hi, I have started taking Ginette 35, the 21 days pack. I have finished the first set of pills. My doctor has asked to give a gap of few days and then start again from the second day of my period. However, I wanted to know what are the chances of pregnancy during these tablet-free days. What precautions I need to take if I have unprotected sex.
Also, I am suffering from breast tenderness and pain because of this tablet. Is this normal?
Thanks in advance