Single Kidney Long Term

Hello all.  I'm Jessica.  I am a five year breast cancer survivor who donated a kidney to my husband (now EX-husband, lol) six years before my cancer diagnosis.  My one kidney probably faced quite a bit of hardship during chemotherapy but it made it through...although now (just three years after treatment ended) I am starting to have a lot of other health issues.  Just was diagnosed with gallbaladder disease (due to my thyroid...what?) and my kidney doesn't seem to be doing so great.  My last lab was a GFR estimate of 53 with creatinine at 1.2 and BUN at 22.  I KNOW I was severely dehydrated at the time (and struggle with this constantly).  But I am wondering if anyone else has low GFR estimates due to having only one kidney?  Mine has slowly declined in the last year.  I want to make an appointment with a nephrologist (as my oncologist is my primary and handles everything) but wondering if that is necessary.  Is the GFR low due to the scale being for two kidneys?  Do I possibly have CKD?  I'm trying to stay positive but I'm concerned.  My creatinine number has stayed steady between 1.1-1.2 after surgery.  My BUN has moved up and down a lot, presuming due to water intake.  I am very active and go through periods of eating perfect and then get stressed and eat bad on occassion.  At 41 I never imagined all of this. At 35 I never imagined cancer, especially after my health was so good I donated a kidney!  But life is funny.   I paid attention to everything!  I also recently had to undergo a total hysterectomy due to the breast cancer risk. Maybe the menopause affected the kidney function?  Again, staying positive as always, but looking for any insight you may have.  Thank you all for your help!  Sending you happiness, health and healing!