Help!

Alli • All I'm saying is keep your bad vibes out of my cornflakes
So my guy and I haven't really been together too long (probably 3 mos.), and well? I just got my period last week for the month. Not a big deal, except that for some reason this time I was beyond irritable and moody and irrational, which has happened before but not to the extent of what it was this time. 
The problem is, I ended up yelling at my guy several times and getting angry at him for no reason and he's pretty upset about it. And I don't know what to do to fix it, but losing him is not something I particularly would enjoy at the moment. How do I fix this?