"Diagnosing gallstones at kettering general hospital"

my mother went for a scan on in early december 2011 as she had stomach pain. she has had this for approx 4months . about 10 days later my sister was told the scan was ok and nothing was wrong. my mothers pain was getting worse and a few days later we had to call out a ambulance because she was doubled over in pain. she is elderly and decided not to go to hospital. only last week we had a doctor out on friday and saturday because her pain was severe. she was diagnosed with constipation. yesterday 7 weeks after the scan we got a letter stating my mother has gallstones.

what i would like to know is why has it taken so long to diagnose this problem.