Just found out I’m pregnant 😍😍 but......😔

so I just found out Friday (the 18th) that I was pregnant. Took two tests came back positive, immediately went to the ER (why ? Idk🤦🏽‍♀️) and there they confirmed through blood work and a pregnancy test, that I’m pregnant,... went down for a ultrasound, they weren’t able to see nothing, went to the doctor (yesterday) had another ultrasound, still nothing, they gave me a pregnancy test at the doctor as well, and it was positive too, and they also took blood from me as well I guess to detect how many weeks I am ... is there any reason why anything didn’t show up in the ultrasound? I understand it may be early , but I ATLEAST thought the sack would be seen... any thoughts ? Or experiences with this ? Should I be worried ? 😫😫😫 this is my 1st pregnancy by the way !