Question about previous vet help: did the vet do any lab work to assess the right antibiotic to use? Or did they just take a guess? It matters, & if not, maybe the first RI was never fully gone.
Also, it's no surprise that your snake stopped eating for a few months after that- injections are stressful, vet visits are stressful, & antibiotics destroy their "good" (necessary!) gut bacteria right along with the infection it was intended for. They can impact the snake's appetite, for sure. For best results, AFTER antibiotics are given, it can help to add a reptile probiotic to their food for a while (like Nutribac or Bene-Bac) so they regain better digestive function, & FEEL like eating again.
Question about your wood vivarium- is the wood well-sealed against moisture etc.? If not, he may be re-infecting himself. Unlike glass or plastic, wood absorbs a lot more than just moisture, & many pathogens thrive in a warm humid environment like BPs require.(Ask your vet about this too.)