You have not mentioned how the urinary infection was diagnosed. If urine examination was done and it is showing pus cells in urine then infection is likely. If he is not responding to the antibiotics then urine should be cultured and treated with appropriate antibiotics.
There is a possibility that your fathers symptoms are because of prostatic enlargement. Prostatic enlargement can cause irritative symptoms like frequent urination
, urgency, pain during urination. Also check his blood sugars. He needs to visit a urologist