Terrified

After a miscarriage and a blighted ovum (2 losses) I'm pregnant again and this time was a surprise, I was told by my ob that I should wait a year before trying again. And when I got the positive test...all these emotions and thoughts just took over. I am having a hard time being happy, I feel like this is just gonna end like the last two and I cant shake those negative feelings. I want so badly to be happy and to be able to celebrate but all I feel is dread for the first ultrasound and the moment the doctor tells me that I'm not going to have this baby. I dont want to get my Hope's up just to have them crushed again.