What Causes Burning Sensation After Urination?

Hello, I am a 17 year old Female. 5 foot 7, and 150 pounds. After I urinate sometimes, I just feel a slight burn, Its bearly noticeable... Usually it happens only around the afternoon. This has happened the last couple of months, and after I drink an adequate amount of water a day it goes away. Well today, I have not drank water but yesterday and the day before I loaded up on water, and I feel a slight burning sensation after i urinate. It lasts for at the most 2 minutes. But I am still kind of worried. I am thinking maybe it is because I am ovulating, but i really do not know. I have gotten tested for all STDs in the past and they came back negative, but I have never discussed this problem with my doctor. Please give me some advice.