first scan and there was nothing there ????

ok well i went to my docs this morning and he did a urine test and it was positive and he also did bloods which i wont get until tomorrow but he sent me for a ultrasound because of my miscarriages in the past and she told there was nothing there and it could be to early or something other than a pregnancy ???? what else could it be ?? if all the urine tests are positive straight away shouldnt there have been something there im so down and 2 morrow seems like forever away for the bloods , has anyone ever had this problem and if so what was the outcome thank you so much in advance ann xxxxx