okay so im almost 21 years old and this whole time im thinking my periods are normal. but im starting to wonder other wise. i typically have 30 to 31 day cycles. my period will either come 4 days early or some days 7 days late. when i have cramps on one side it severly hurts one side of my lower back to the point its like a big needle being put in it. my mom had endometrius as did her sisters and mother. is this a normal period thing or should i be concerned?