I see someone else mentioned it too.
And some people said cranberry juice. Good too, but don’t use any with sugar in it. I think d-mannose is better.
One last thought: If you have pain, go straight to an MD and don’t mess around. Back pain tells you it has already spread to your kidneys. If you have the usual weird urinary symptoms and no pain, it’s PROBABLY OK to treat it yourself, but it may not be.