This one better not wait, please go to A&E or call 995 now if the rash is spreading quickly, you're having trouble breathing, or your face swells up. Otherwise, since your polyclinic doctor is already referring you to the dermatologist next week, I'd keep an eye on it in the meantime and try not to scratch even though it's itchy. During pregnancy our skin can act up in weird ways, so the derm will be able to figure out what's really going on. In the meantime, stick with plain water to wash and maybe a gentle moisturiser so you're not making it worse.