Having a problem with l odor, even after washing! How to fix & whats the best material underwear to wear?

Okay, im 16 and Ive had a slight l odor for a good year now. Ive been to the doctor and was told I have absolutely no infections or anything. I wash with water and a very mild soap, as I know strong scented things can mess with the pH balance. Ive never douche or anything of that nature. Why does my have an odor? I wash at least once a day and the area is almost completely shaven so the hair isnt collecting odors and sweat. Are there any sprays or anything safe to use down there that will keep me smelling fresh constantly? Also, Ive heard its best to wear cotton underwear. Is this true? Is it just as safe not to wear any underwear or does that leave more room for bacteria to enter? Please help here!!! I have no one who I can talk to about this. Thanks in advance.