Gfr declines with age. If this is an egfr (estimated from creatnine) is might be reflecting high protein intake or low hydration. Muscle loss (temporary or not and sometime medication related) is another factor that can increase creatnine levels. Collage supplementation and creatine supplementation can affect the blood levels of creatnine. Biotin can affect the assays used to measure creatnine.
You might request the cystatin test said to be more reliable, or request a second creatinine test. I suspect that the CKD of your diagnosis is a numbers game rather than kidney disease.

If your GP and his assistant tell you contradictory things, if I were you I would go to a different doc! You might simply be dehydrated when you had the blood / urine test but it is worth retesting. I have my eGFR tested every 3 months (I buy the test from Quest or LabCorp online).