Pain in lower left abdomen & groin area.

I had pain in left side of lower abdomen and groin area which can radiates till testicle .Pain is simetimes mild and sometimes severe. Consulted urologist and he predicted Stone in Bladder and aksed for USG KUB. In USG no stone detected in bladder and one small stone( 2.3mm)  detected in Left kidney. Doctor saying that you may have small stone in bladder which is not getting detected.He gave some medicines and asked to come after15 days with USG one more time. I am really not satisfied with his statements and hence want to ask : 1.Can stones go undetected in KUB USG ? 2.Why he asked for USG again? 2.Is there a strong possibity of having stone in bladder if you have stone in kidney ? 3. What other reasons can be there of pain ? 4. What should i do next ? Please help