Bleeding and went for a scan and got told there can not see nothing in the sack

Hi can some one help me I am meant to be about 7/8 weeks pregnant started to bleed on Sunday went for a scan on the Wednesday to be told there can not see any think in the sack but toke bloods and my hpg is still high so there want me to go back next week for re scan has any one ekes had this happen to them