PMS RELATIONSHIP TROUBLE

Natalie
Help! 
My boyfriend and I usually end up fighting over everything while I'm on my period.
I think it's a combination of several things
1. I'm emotional but it's more of just irritation and overreacting to things
2. (And he has agreed to this) he gets really irritated with me and frustrated while I'm on my period. 
3. I don't think he understands how emotions and stuff like this works throughout the month. I've tried telling him that I have exams this week, I'm on my period, and we are dealing with another stressful situation... But he isn't being very nice about it
Maybe it's just me thinking that.. 
Please give tips on how to not let PMS ruin your relationship?!
We have a horrible week on period weeks. We've made it through about 25 months now though - but would like to ease the intensity of period week problems!