Wah this one I also kena before during my second pregnancy lah! My friend went to her gynae about the same thing, small itchy bumps behind the knees, and the doctor mentioned it could be PUPPS, which is quite common in pregnancy, nothing too alarming, but still worth checking. Someone in my mum WhatsApp group also warned that if the itching starts spreading to the thighs and arms, it's better to get checked faster because her cousin had that and they found out it was something related to the liver called cholestasis, she said the doctor told her itching can sometimes be a sign of that, especially in second or third trimester. For relief in the meantime, a few mummies tried oatmeal baths and calamine lotion, some said it helped a bit, some said not shiok enough lah, but at least cooling. So honestly, both sides lah, could be harmless skin thing or could be something needing more attention, I would personally just go see the doctor to be safe rather than tahan and wait. Better let your gynae or GP take a proper look and rule out anything serious, especially since you're pregnant!
Pregnancy can sometimes make skin conditions like eczema, heat rash, or general skin sensitivity flare up, and the backs of the knees are actually a common spot for that 😊 If it's just mildly itchy and has only been there for a couple of days, you could try keeping the area cool, avoiding harsh soaps, and using a gentle fragrance-free moisturiser. You don't necessarily need to rush to the clinic, but do get it checked if the rash is spreading, becoming painful, looks infected, or if the itching becomes severe. Hope it settles down soon!