What Causes Stabbing Pains In Vagina?

I am 27 years and a mother of 3. I had a tubal after my last child, 4 years ago. I am have occastion sharp stabbing pains in my vagina that stop my in my tracts for several minutes at a time. I have recently had an STD test, all the results are negative. I am really embarrassed to bring it up, because there isn't anything that I can think of that would cause it. Do you have any solutions or advise?