First child and 38 years old.

I am mostly worried about amniotic fluid because I haven't been able to keep down liquid. Any my tummy is still rather flat, many friends commented I didn't look pregnant at all.

I am week 20 now, next appt will be Week 23. Will it be too late? According to brochure it's to be done week 18 - 20. Dr suggested like one month ago but she was in a rush and didn't seem to emphasize it, and I forgot after all the excitement about passing NICC test.