hello.sometimes its difficult to say on clinical examination which organ or syatem is exactly causing the problem due to close proximity different organs.
your lower abdomen pain could be due to kidney
stone but some stones do not cause much pain and your urologist
must be thinking in the same lines afterall i believe he examined you and then advised to see a gastroenterologist.
a gastroenterologist will look for GI tract causes for abdominal pain
, may advise few tests or investigations.
so you have advised a correct tract and its worth seeing a gastroenterologist if urological cause is ruled out.
all the best.