Sometimes blocked hair follicles can become infected and cause little pustules.
Pustules can form anywhere on the body. People with greasy skin are more prone to these forming. They are like little acne spots.
If they are infected the doctor can help with prescribing an antibacterial cream rather than an antibiotic because of the pregnancy.
Could it possibly just be an ingrown hair?
Could be just the little sweat glands that we have down below that are slightly inflamed.
I am surprised the doctor did not give you anything for it to alleviate the itching.
Do not use any harsh and drying products like soaps, bubble baths, shower gels and the rest down below. Wash with water, baby washes should be fine. If the doctors have ruled out thrush, or any bacteria, you could try Lamasil to help stop the itching.
Natural yogurt applied down below will cool down the area.
You may have developed an irritation to the washing products you are using. Also use a non-biological washing detergent. I trust as you are pregnant you are not wearing any tight clothing. Also wear cotton underwear which helps the body to breathe and are better than the manmade fabrics that make you sweat.
Enjoy the rest of your pregancy and wishing all the best.