don't sleep on doing some actual physical therapy stuff alongside the belt - that's where a lot of people miss out. the belt alone can feel good in the moment, but strengthening your core (yeah i know that sounds counterintuitive when pregnant) and stretching your hip flexors actually addresses what's causing the pain, not just masking it. your doctor or a prenatal PT can give you moves that are safe at 5 months and make a real difference.
that said the belt does work, just maybe not the way you'd think. it's not magic but it redistributes how your body is carrying that weight, takes pressure off your lower spine. some people get immediate relief, others notice it more after wearing it consistently for a few days. the trick is finding one that actually fits right - too loose and you're basically wearing an expensive piece of fabric, too tight and it's uncomfortable. maternity-specific ones are worth it over generic belly bands because they're designed for how pregnant bodies actually change.
one thing the others didn't mention: timing matters. standing for long shifts is rough on your back anyway, and pregnancy just amplifies it. a belt helps but also try taking breaks to sit, shift your weight, maybe lean against something. the belt's doing some of the work but you've gotta not ask it to do all of it. if it's still brutal even with the belt after a couple weeks, definitely loop back with your doctor since sometimes back pain signals something else that needs attention