What Causes Frequent Urination And Diagnosed With UTI?

Suddenly, I had the urge to urinate frequently. I went to dr and was diagnosed with uti. I have no pain, just burning when I urinate. The dr said it was really minor according to urine sample. No blood in urine. I noticed the burning during sex but NO pain. I figured it was from not using lubricant. The urine frequency has gone down and the burning is better. I am taking cephalexin 500mg, pyridium 200mg, and flagyl 500. Arent these the same symptoms of bladder cancer, even though theres no blood in the urine. Is water intake important at this time?