4 postives but no baby?

I'm after some advice for a friend, she's done 4 pregency tests deffo strong positives, she went to the woman's health today for an emergency scan and there was no baby no sign of even being pregnant!! so according to the lady even tho my friend has had 4 strong positives she never had a baby in the womb and its not a eptopic becuase they have checked, she's done a clear blue digital this evening and it deffo says pregnant 1-2 weeks, has anyone else has similar and not been pregnant or been pregnant and the baby is playing hide and seek maybe? thanks in advance x