Why if you go from anal to vaginal sex you get a urinary tract infection? it's the second time it's happened?

Because: The rectum is loaded with e.coli (and other bacteria) so this gets introduced directly into the vagina, leading to a urinary tract infection.

Location: The reason is the very high exposure to gut bacteria. Some of the bacteria that cause urinary tract infections are bacteria that live in the gut (E. coli, enterococcus). The opening to the urethra, where the urine comes out, is close to the vagina. The bacteria get into the urethra, and from there into the bladder, where they can cause a bladder infection (cystitis).