Talk to General Physician on Low Urine Output And Dark Color

From last several months, I went through a change in my urine. Before this problem, urine output and urine color both were normal. Suddenly, my urine output decreased. Its color also changed to yellow and sometimes very dark yellow. I was already drinking enough water but increased my water intake. But urine remain same. Urine analysis report showed slight infection, took antibiotics and citro soda (as prescribed by doctor) but nothing changed. I drink a lot of water but it seems that water is not being absorbed properly. Normally I do not feel any pain while urinating but yes I feel a little bit in penis whenever the urine is very dark. What do you doctors think the actual problem is?