Can you help?

my nan has had bad pain under her rib cage which moves to her back ,we have taken her to her gp 3 times and they have now said she has shingles, but we are not convinced. It hurts when she moves and wakes her at night ,she cries with the pain . Does any 1 know what it could be .She does not have a rash like you do with shingles ,she is 83 and horrible to see her in so much pain