HCG levels very high

On Friday afternoon I went to the emergency department with really sharp stabbing pains and head spins. I recently had a miscarriage and was scared I was miscarrying again as I fell pregnant straight away after my first loss. Thank goodness I wasn’t and I got to see my little blob and I am measuring 5w 4 days but my HCG levels were 19000 is that normal for a singleton pregnancy.

I know it’s crazy but I just had a feeling this pregnancy was going to be twins. Also has anyone gone to their 6 week scan and only found one baby but have found they were pregnant with multiples at the 12 week scan?