I'm experiencing exactly the same thing and did so with my previous two pregnancies. I just keep expecting to see af type bleeding everytime I go to hte loo! I'm also 5 weeks so don't panic. I also had this kind of pain at 8 weeks when my period would have been due, so expecting the same type of pain then this time as well.
just try and relax.
Apparently it is just the uterus stretching according to the dr and is a good sign. I do not have any other pregnancy symptoms, even did another test yesterday becasue of abscence of symptoms.