Total liquid diarrhea & painful/strong intestinal cramping on 2nd day of period. no nausea or other symptoms & never had this before. period related?

Maybe, but get eval: First define the problem (do you have soft or frequent stool?), any other circumstances in which diarrhea developed (malabsorption, pancreatic maldigestion, food intolerances, stressful times, exposure to ill individuals, food poisoning, ischemic gut, inflammatory colitis, etc.), severity (stool volume, dehydration, blood, night-time awakening, weight loss), duration/ recurrence, ?history of IBS.