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The abscence of bile and gall bladder
may be the reason of having grey stools if they are soft and you can pass it easily and regularly.The problem of bloating
of abdomen and nausea
and even frequent headache can be due to gastric problems which is a common occurring in people who have been operated and had their gall bladder removed.Also a big disturbing factor is a stage 4 kidney
disease so the better person to advise you regarding the medicines you can take will be your Nephrologist
(kidney specialist) so consult him and he may give some medicines for your stomach problem.