3rd pregnancy

This is my thrid pregnancy my other two ended in a miscarriage. Everytime i have went in to hear the heart beat there isnt on or they couldnt pick it up. Im extremely worried for tomorrow it will be my first ultrasound with this pregnancy. Ive been praying like mad to have this my sticky baby but im extremely scared. I dont want it to be like the others. Its hard for me not to be in my head about it all. Plus i dont have any symptoms yet besides my boobs. God please let tomorrow go well please let this be my rainbow... keep me in your prayers please