low HCG

I'm not sure the exact date I ovulated but my period was due on 3/12 and never came so I took a test and it showed a vvvfl so I called my OB and he ordered a HCG blood test on 3/13 and it came back a 9 !? 
They want me to come back on Thursday 3/16 to see if it goes up.
Has this happened to anyone else ?