HCG level were 9 still Positive Test

Shaina • My husband and I are trying to conceive our third child.
Wednesday I went to the ER because I was bleeding and cramping at 4 weeks and 2 days. Got a blood test came back positive but my levels were low (9) but how are my levels that low and I'm still getting positive tests to this day. 
I was told I was miscarrying or having a threaten miscarriage