Tender boobs and what do they mean?

Rachael
So my boobs have been very tender lately as in the past 2-3 days. Anyway I'm due for my period tomorrow according to <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">Eve</a>. Now about 10 days ago I had protected sex and I didn't know if this was a sign of pregency. My mom always said the tender boobs were the first sign but I also thought hormones could be a possibility since my period is coming. Also when/if I get my period tomorrow, does that mean I am 100% not pregnant ? I know these mah sound like stupid/silly questions to ask but it will make me feel better.
Thanks for everything. 
-Rachael