How to apologize to a guy for getting mad during your period

I got in a fight with a guy I'm dating yesterday. This was over my dog (posted about it). I've been On m period and I think it's what made me go off on him. I'm not one to ever blame my period, but I have felt extremely moody this period. How do I apologize? Do I tell him about my period (we just started dating so I feel like it's tmi).