persistant itching/irritation for 3 months.

im stuck as to whats going on with me down there..... For three months now I have had a irritation down there. Its like almost a tingling sensation that won't go away. It all started after I masturbated one night. At first I thought my hands werent clean enough and i irritated myself and had a yeast infection. Well three weeks later i went and got tested at a clinic for stds and hiv. All were negative, although they didn't test for herpes or hpv. Which as far as I know no one I have slept with were infected with those and I had a monogomous relationship with no prior irriation for over a year. And I have never had blisters/ unusual bumps/itching/irritation before this masturbation night.

I have also always gone for a yearly exam and pap everything being normal. While at the clinic i mentioned the itching but the nurse seemed to think it was a normal irritation from looking and that it would go away on its own. Well it never did.
The irriation is most persistant in the around my anus. On one side of the opening of my vagina, and also the inner part of one side of my vaginal lip. Anti itch cream seems to help, but it just stays the same? I can't take this anymore im planning to see a doctor soon, but in the meantime any help?
I do shave and thought it was from that it seems to get better when i don't shave as often, but still is there, WHAT IS THIS?