Thanks for posting your query to HCM.
I can understand your apprehension and stress
related to the problem which is disturbing your sex life.
As per the history given by you the only disease causing the whole series f symptoms is Candidal / Yeast infection. As per your history you have been tested for STD's, but hae you been tested for the Candidal infection. Even if you are been tested mild form of Candidal nfections are actually not diagnosed so frequently. This can manifest exactly the same symptomatology as you explained. You can worth try vaginal pessaries to be used at night (available as over the counter drugs) and oral treatment if is not getting better.
Vaginal douches two- three times with saline water mixed with gentian violet paint ( 1:1000) for 10-15 minutes daily ( this is a simple method where you take bath tub half filled with luke warm water and add pinch of salt and few drops of gentian violet paint). Abstain from sexual activity for at-least 15 days and after that use condoms strictly during every sexual act. Your partner may also need the treatment if you experience recurrence of symptoms once treated.
Hope to give you the best advice do give us the follow up,
With best health wishes,
Dr Sanjay K Kanodia
Dermatology & STD (Venereology)