What Does Back Ache On The Right Side Indicate?

My mom is 83 and had a hip replacement 5 years ago and had had a kidney that doesn’t drain all the way which a stent was put in at the time and later removed. Went to the urologist today and had a ctscan and her kidney is fine. Question is... could this be her hip? She does complain of moderate pain with one night of severe pain. She says some pain has gone her leg but always. She also complained of not going pee as often as normal even though she has been drinking the same amount of water a day. We don’t know which doctor or specialist to lean towards for help. Her general doctor makes her feel like the pain is all in her head and she doesn’t want to go through a pile of useless tests if we can narrow down what it might be. It’s on the right side of her back only. Which is hip replacement side.