I had this with DD2 and it lasted for about a week and a half. I went to the GP who ordered some blood tests and ultrasounds - the bloods confirmed that HCG levels were rising (which is what you want) and the u/s confirmed there was a blob with a heartbeat. I had 2 blood tests and 2 ultrasounds a week apart for comparison. In the end everything was fine and there was no real explanation for the bleeding. I was told to rest and take it easy so we didn't DTD until things settled down and I didn't do any exercise other than walking.