What Causes Cramps 2 Weeks After Periods?

hi i am 25 and have 3 kids the youngest is 3yrs my period has changed alittle instead of 7 days its like 4 days and very light and its been like that for a few months now...i also noticed that a week or two after my period that i am crampy and that seems like it lasts for like two weeks or so and lately i noticed that when i poop blood comes out of my vagina just alittle bit and i was wondering why that would be happining?