Frequent urination, unable to empty bladder, urine infection. On antibiotics. Treatment?

I have a query on behalf of my father. He is 72yo and has been diagnosed by his GP as having a urine infection. This was approx 2 weeks ago. he was prescribed antibiotics (6) for three days. His symptoms did not improve and he went back to his GP and he was told that it was a urine infection and prescribed the same antibiotics for 28 days. 9 days later he is not any better. He is still urinating 5,6,7 times per hour even through the night. He has no control over when he needs to go It does not hurt to urinate. he only urinates a small quantity each time