My period started on December 31st and ended January 4th,I want to know if this periods counts for both jan and December,or was I supposed to get a period for January? Two weeks ago I had a stabbing pain in my right abdomen and it traveled all the way up to my right breast and it was hard for me to sit up,and a week ago I had pains on both my abdomen sides and also suffered back pains,at 1st I thought I was gnna get my period but nothing happened,until now February 2nd.what can be the problem if there is one.. I'm 21 and don't use any birth control and I am sexual active and not preventing. Please answer ASAP!

How regular are you periods usually? I think you might be pregnant. Take a test about two weeks after you should have gotten your period. As well, I think you should be your back checked out by your doctor or a chiropractor. I don't think the two are related.

Periods aren't counted for months, but the time between them. IF you have a solid 28 day period then you will have a few months where your period will be at both ends of a month.