I Want To Cry Just Before Mentration And Its Really Embarrasing

I want to cry just before mentration and its really embarrasing!? I dont know why this happens but at least i see a pattern. Just before my period i want to cry, i mean i really cant control it. Worst of all i was in work yesterday and out of the blue i started tearing up for no reason. All my work collegues where like whats wrong and my boss thinks i cant cope with my work, thats not true but how do i explain im crying for no reason. My boyfriend doesnt get it either so i get angry with him when he thinks hes done something and i cant explain why ive got tears in my eyes. Im not a sentisive person. Anyone else like this.