Could be thrush.
You are more at risk of getting thrush while you're pregnant. Changes in the levels of female hormones, such as oestrogen, increase your chances of developing thrush and make it more likely to keep coming back.
Perhaps ur doctor did not prescribe oral treatment because it may affect your baby.
Perhaps u can ask for an anti thrush cream to apply around your vulva but be sure to have it prescribed and not buying it off the shelf.
Not all of these products are safe to use at different stages of pregnancy, so it's important to talk to your doctor and pharmacist before using any products.
Perhaps get new undies, and yes cotton is always the best. Wash underwear in hot water and pure soap and double rinse to make sure any irritants are removed before you wear themI
If your using panty liners, avoid scented ones and change it regularly.
Avoid fitting clothes luke tights or jeans. Avoid using soaps, bubble baths, bath salts, perfumes and perfumed talcs around the vaginal area. And never ever use anything harsh such as disinfectants even diluted, near your vagina.
After wash, always wipe from the front to the back after going to the toilet since this stops bowel organisms being swept into the vagina. Don’t use perfumed toilet paper because it can cause irritation.
Keep dry before using ur undies back again.
Hope these helps .