Pregnancy tests are not reliably positive until two weeks after
a missed period. With that in mind, you may be pregnant. Breast tenderness can be a sign of an imminent period or of early pregnancy. However, nonspontaneous nipple discharge is a common, benign issue for many woman, pregnant or not. It is usually bilateral (on both sides), like yours and can be clear, white, yellow, or even green.
On the other hand, spontaneous discharge (discharge without stimulation) usually means something is wrong, and that you should go to your doctor as soon as possible. You would need to be further concerned if spontaneous discharge was from one breast only, was bloody, or if you also noted a breast mass. NOTE: it is not advisable to check for breast masses during your period, as the breasts are usually more "lumpy" around that time anyway. Your case does not sound like a pathologic case of nipple discharge. I'm including this second paragraph only for your information at this time..
Consequently, my recommendation is to cease nipple stimulation and wait patiently for your period to come, or not - *smiles* - and you may be pleasantly surprised in a few weeks. Good luck, and thanks for the opportunity to answer your question. Here is an informative document on nipple discharge for your further perusal: http://familydoctor.org/online/famdocen/home/women/reproductive/breast/673.html