Kidney GFR

My doctor has asked for another Kidney function test this month as the last one fell at 65 almost a year ago. My cholesterol was slightly raised (my mother has to take statins for cholesterol and she has an underactive thyroid) if this is relevant.  Now though I am becoming increasingly worried as this could show possible kidney problems.  I have been experiencing a very sharp and acute pain in my pelvic region for going on two years now.  I have had a bowel endoscopy, ultrasound, urine test and nothing un-toward has shown up.  I am wondering if this pain is connected to kidney problems although I don't have pain in my kidney area.  I have a had a few unexplained joint pains from time to time.  About 8 or 9 years ago I was on Lithium 400mg (I think) for slight bi-polar which lasted for around 3 years, so for the past 5 or so years I haven't taken it and I had regular lithium level tests at the time all of which were normal.  But now my mind is racing looking for answers and I feel low thinking I may have a kidney problem. Could you enlighten me in any way.  Thankyou.