Based on your report, suggesting that "a full common set of STDs" is already ruled out, I assume you were told that you are negative for HPV, HSV, CMV, chlamydia, gonorrhea, or syphilis. However, from your posted/emailed snapshot I notice a heavy discharge, more indicative on the mixed bacterial infection.

Below are plausible remaining causes for your bumps - both venereal and non-venereal:

(1) Skene's duct cyst - occurs on either side of the urethra, mostly with a diameter < 1cm, and mostly asymptomatic; in rare cases may complicate into an abscess, at which time a surgical incision is required with application of a broad spectrum antibiotics (Keflex), or marsupialization;

(2) Bartholin cyst - occurs on either side of the labia minor and can reach to the size of a walnut; symptoms include painful swelling adjacent to introitus, usually at the 4 to 5 o-clock positions; mostly contains gram-positive and anaerobic bacteria; the cyst may drain spontaneously; management includes warm seat baths, incision and drainage (marsupalization);

(3) Nuck hydrocele - a mesothelial cyst full of serous secret; should be managed very carefully as may have a link to the round ligament;

(4) Blocked hair follicles - the bumps are often irritated and tender; management includes antibiotics, large incision, and drainage;

(5) Clogged sweat glands (Hidradenitis suppurativa) - usually antibiotics are required;

(6) Fox Fordyce disease - a condition that causes non-tender clogged sweat glands with pruritic discharge; treatment includes steroid creams, antibacterial applications, laser therapy, and other more specialized means;

(7) Sebaceous cyst of labia minor - small lumps under the skin; those are closed sacs that contain sebum (oil); these are often inaccurately conflated with epidermoid cysts, which by contrast, contain keratin and have a foul odor;

(8) Lastly, several infections that are not included in the routine gyn- screening -

- Molluscum Contagiosum, a viral infection manifested in small, pearly-color, fleshy bumps on the vulva with a central indentation; usually disappear without treatment;

- Haemophilus ducreyi - a bacterial STD (gram-negative coccobacilli) - also known as fake chancroid; is commonly accompanied with enlarged inguinal lymphatic glands (a distinguishing sign from the viral Molluscum); the bumps are painful, mobile, by contrast to the chancre in syphilis; treatment includes macrolides (Azithromycin) and third-generation cephalosporin (Ceftriaxone).