What Could Be The Cause Of Abdominal Pain In My Dad Having A History Of Kidney Stone And Showing Rbc Cells In The Urine Test ?

hi, my dad is 65 years earlier he was having stone in his kidney but then he had a laser operation around 4 years ago then again we found stone again in his both of the kidney .Recently he had ultrasound nad we found no stone in his kidney> bt from last 2 weeks he is having some pain in his lower abdomina> we have gone through all tests and found some rbc cells in his urine . he had gone through CT of his lower abdominals but didnt found any prob in it . can you help me know what problem is he suffring from . hi, my dad is 65 years earlier he was having stone in his kidney but then he had a laser operation around 4 years ago then again we found stone again in his both of the kidney .Recently he had ultrasound and we found no stone in his kidney. But from last 2 weeks he is having some pain in his lower abdomina. we have gone through all tests and found some rbc cells in his urine . he had gone through CT of his lower abdominals but didnt found any prob in it . can you help me know what problem is he suffring from .