Miscarriage or not ...

I am supposedly 4-5 weeks pregnant .i tested positive for pregnancy tests 4 times with the first being last weekend . Today for the first time I had very very mild Spoting. Basically when I pee I have very tiny red threads in it . Like very tiny blood threads or something . I went to the ER and they checked my HCG levels and it was 19 . The doctor has asked me to get the levels checked again in 2 days to see if they are rising or not . He said either it was really early on in the pregnancy or I was having a miscarriage in which case the levels will further go down . They also did my ultrasound and Transvag  and saw nothing .i am so tensed can't think of anything else . Anybody had any experience like this ?