i am 5 weeks pregnant but since 2 weeks i am having light pain in my upper stomach and severe backacke is this a problem

Um... are you saying at 2wks pregnant?

because if so then it just isn't possible.  The 2nd week of any pregnancy is the same as if on a regular cycle...your body getting ready to then actual ovulating... 

so two weeks would be around the time you would ovulate- at which point there is no fertilization. 

Also, your uterus/ovaries are located low on the trunk..behind the bladder.  If there is pain in your upper portion of your trunk then that wouldn't have anything to do with pregnancy in the general way of things. 

If you had this pain in the first two weeks of your cycle then I would say that most likely has another reason behind it.