Creatinine and urea increase as the ability of the kidneys to filter fluid within the body declines.
This is irrespective of the cause of reduced efficiency of the kidneys.
The most common reasons for developing raised creatinine levels are when the filtration mechanism becomes gradually damaged by long-term raised blood pressure or diabetes
Since your father is showing consistent rise in serum creatinine
levels after the surgery,it means that functions of kidney are deterioring and so he should be investigated thoroughly for finding the cause.
Consult a nephrologist
as early as possible.