What Causes Vaginal Itching And White Patches Around Clitoris?

I ve been having vaginal itching off an on for years now. In April it became very severe, & was accompanied with major swelling and sores which some of them I m sure where due to my scratching. I went to the doctor who just assumed I had a yeast infection and prescribed some oral meds. It went away, but I have been having some itchiness still off and on which became severe again recently. I was prescribed the same meds but it did not help this time. Upon examining my vagina (even in the past) I noticed that I have some white patches on my vulva and white thickened patches around my clitoris. (Even in the past over the years when I would scratch when the itch would be so severe, pieces of the white thick skin would come off.) Could all this be part of a yeast infection? Also, I should mention that I never had any white or cottage cheese like discharge. Also, I have been tested to STD s and none have been found. So am I still looking at a yeast infection or could there be another possible cause?