CREATININE. Need to consult if required.

Hello Dr...From last 7 months I am facing some issues..In JAN MY KFT was normal which was done as a regular routine blood work...In May for the firat time in 3 years increase in CREATININE upto the highest limit of the lab was seen...Doctor suggested that it is within the range so no.need of worry (1.39...Lab range was 0.6-1.4)...I repeated that test for every weekbin the next 2 months...It never increased from that value and comes to 1.17 once...Then I contacted another doctor who uggested for urine tests and USG which all comes normal...Only MUCOUS THREADS were seen...He said that all is f9 Now...I am facing a discomfort in my left lower back...Initially it was limited to the lowest part...Now It is reached upto the Kidney area along with left side...Also I am facing some urine issues...Urine output is almost equal to the liquid intake...But frequency and stream of urine is changed...Kindly guide what can be the possible reasons...and which speciality I need to consult If required.