Same here and im only 3 weeks!
Very possibly implantation cramps...my back hurt sooooo bad (with no bleeding) i thought i was miscarrying and i was around 5 weeks...it lasted like 2 days...im almost 14 weeks now :)
That happened to me too a few days ago. I'm six weeks now.
Implantation has already occurred, otherwise she wouldn't have a positive test. If the pain is severe, you need to get it looked at by a doctor or at the ER.
However...implantation can take up to 10-13 days to complete and you can test positive after the 1st day of the implantation process starts due to hormonal changes...
If its really bad, to where you double over in pain, that means something is wrong. I miscarried at 5 weeks a few months ago, but didnt know until I was 10 weeks. I didnt have any bleeding so didn't think I was miscarrying. Definately see a doctor. Hope your not experiencing one though, goodluck.