What Causes Breast Discharge Near A Menstrual Period?

I am female, I am 24 years old, I am 98lbs. and that is my normal healthy weight, I am about 5'4". I am healthy and I have decided to try to have a baby so I am taking a prenatal vitamin. I have noticed that sometimes around my period and around when I may ovulate that my breast will have some light discharge. I is from both, it is clear or slightly green, not sticky or smelly and it happens more when I am aroused or my breasts get stimulated. I can squeeze some out by hand or sometimes if something rubs my nipples a bit comes out. Is this normal?