I Have Been Checked For STDs/stis And Have Always Came

I have been checked for STDs/stis and have always came back negative. I have found that often times I have a very itchy vagina and I also have white discharge. My gyno always tells me that it is normal but I feel that it is not. Also I have a pimple on my clitorous that is pretty painful. Is there something I can do to make it go away. Could wearing thongs make me continuously get the pimple there BC of the rubbing? Is it possible that in would have something and it just not show up?
Thanks