Positive blood & urine test... But no pregnancy 1 week later??

Has anyone Elese had this problem? AF was due last week (April 28) and never came other than some spotting.  Urine test came up faint but positive on Tuesday the 29th. Had blood taken on the 30th and confirmed I was pregnant. One week later the follow up blood test came back saying I'm not pregnant. Could I have miss carried and still missed my period? Has this happend to anyone Elese? I've been on a emotional roller coaster !!!