I had a lot of UTIs a few years ago. I did a lot of research into treatments and discovered D-Mannose. This is a supplement, easily available online.
It is a type of sugar which cannot be used by the body and is excreted through the kidneys.
Most UTIs are caused by a bacterium called E. Coli.
Once the D-Mannose passes into the bladder, these bacteria stick to it instead of sticking to the bladder wall. They are then passed out when you do a wee.
I have been taking it for over 5 years and have had no UTIs in that time. Previously, I was getting 4 or 5 a year, utterly miserable.