TeenHelp - Help! Period early??

On December first I had sex and we started making out then next thing I know his penis is near me. He touches me for a sec then I say hey let's use a condom. So we did. Then through the 16-22 I have my period. Everything is normal heavy and everything. But I have been so crazy stressed about being pregnant. I don't even know why. He wasnt cuming or anything yet so. and also I have been taking care of my grandfather because he has been home from the hospital and between school and such I have been REALLY stressed. Also, i have been working out a lot. Well I just started my period tonight. Is this bad? Do you think I am pregnant? I wasn't supposed to start till the 18th or so. Then again, I never have tracked my period till last month, I've been using this period tracker. ANYWAY can you please just tell me if I can get my period this early? :(