Overload Problems?

I've been on a diet for about a month now. I feel very good, but when I exercise at home, my stomach suddenly cuts, as if my cycle is coming. And it starts to bleed, it's not abundant, it just marks. Then it stops. The second or third time I get this after exercise. In principle, my cycle is regular, I do not know why it happens. Has anyone had this happen, is there anything to worry about