What Causes Red Spots On Vaginal Gland Area?

Hi, I am 35 and find occasionally a small area on my vaginal gland under my pubic hair that a red spot appears and feels uncomfortable for about 4 days then disappears. I have been to my local gum clinic and been tested for stds. And the tests have come back clear and the doctor has said on examination that it's nothing to worry about and is a blocked gland. I do do a great deal of exercise. Thanks