Please help :( 2 nurses gave me different oppinions and i dont know what to do anymore?

well i found out i was pregnant around 2 weeks ago, my last period was 27th april but since then i been bleeding lightly, i had 2 vaginal ultrasounds ( one a week ago and one yesterday ) they couldn't see anything what so ever not even a sac :( my hcg levels went from 156, 260, 560, 1800 ( 1800 was yesterday ) the nurse that did my ultrasound said " well i cant see anything so i really doubt that you are pregnant " i started crying and she gave me NO support what so ever! then i went to the other nurse and she said " well it could be still to early to see anything, the fact that your hcg levels increased is a good sign" but i dont know what to think :( from sunday my hcg went from 520 to 1800 so that's good right? about 4 days in between the two tests, i now have to go back in 2 weeks time for another scan and i am so scared that they will not see anything once again :( i am scared that there is no baby, what can i do?! i had a miscarriage back in feb 2011 and since then my periods havent been regular so maybe we conceived around the time my period was due but never showed up? idont know why i have bleeding, its not painful but it is very light, on and off... can someone help me :(