When the burning starts, it is really difficult to know whether it's just the atrophy or an infection. If it's a UTI then the dip stick test can detect infection but often there will just be traces of blood. At one time, my urethra became so sore and inflamed I was peeing blood - when my urine was tested there wasn't any infection, so ABs weren't necessary.
I am sitting here, right now, and my urethra is burning a bit - I've just drunk a glass of water with bicarb, so I expect this burning will subside soon - it's about catching it early. When it starts to burn it could be the start of a slight infection which could be cleared easily by drinking lots of water.
Infections tend to start because bacteria from the anus creates a bacterial infection in and round the vagina and this will easily find it's way up the urethra. This is why it's important to keep the vaginal flora in the right balance as bacteria is less likely to take hold. It's important to really clean well after opening the bowels.
Constant UTIs are very common in the elderly because the atrophy must be advanced.
I personally didn't find D Mannose worked but others swear by it.
Do squirt some of the Multi Gyn up inside as well as around the outside - this will really help to fight off any bacteria or thrush. 2-3 applications per day should be enough and once it feels better you can use it 2-3 times a week. Dg x