My sister in law is 15 days late with her period, has been constipated for about 2 weeks, frequent urination with no burning sensation. She's ruled out Urinary Tract Infection and has been having moderate abdominal pain.

I would surely hope that by now she has been to a doctor. She could have an intestinal blockage, fecal impaction or worse a tumor if constipated for 2 weeks. Don't want to scare but with constipation this long you should have medical attention.