Like many rockabilly songs, especially by Elvis, this has its roots in blues. It’s a cover of Junior Parker, who released his version in 1953.
And, like many blues songs, that itself drew significant influence from American folk music. In this case, “Worried Man Blues”, made famous by Carter Family in 1930.
Elvis’ version feels very ‘country’, with its echoing guitar picking and bouncing bass part.
The song actually appeared on the UK version of 1955’s Rock N Roll, released in the US as Elvis Presley with a different track list.