Dysmenorrhea-free Days are Over!

I don't know if it's a good thing or not. But I'm hoping it'll last for a year, cuz my plan is to breastfeed my baby until he turns a year old. But yeah, I had my first menstruation just this morning, since my pregnancy last Aug. I purely breastfeed my baby, mix direct latch and pump, maybe it's the reason why my body stops making a lot of milk and lessen the hormones that stops me from ovulating. Hello Cramp days... But anywys, my questions in mind are... Is it true that having a menstruation is a sign of decreasing milk supply. Is there an effect in the milk supply when you're on your period? Will my menstrual cycle be back to normal or is it still irregular?