What Causes Burning In Urethra Along With Frequent Urination?

I m a 36 year old female and in pretty good health...I m also a vegetarian and eat mostly organic. I ve had an urgency to urinate for the past three weeks and a burning sensation in my urethra. I also am waking up in the evening regularly to urinate several times. I took a UTI test which was negative and then a culture which was also negative. I went to a urologist today and he said that he thinks it s an over active bladder. I ve never felt like I was going to urinate myself or a sudden urge out of the blue... From what I read online it said that an overactive bladder doesn t cause pain and burning sensations. I was concerned that I might have IC but he said he didn t think so. He also took a picture of my bladder and kidneys and said they looked fine. I m just wondering when this burning sensation will go away and if he made the correct diagnosis? I m very nervous about IC and the information I read about it and was relieved to hear that he thinks it s an OAB but now I m doubting...thanks so much for listening.