it sounds like you need some anti bs, however, as the others have said cranberry juice is the only way along with litres and litres of water as this dilutes the infection and helps pass it.
I drink cranberry squash as you can drink more fluid this way, however, you can also purchase cranberry capsules from the health food shop and if you are prone to cystitis this helps keep it away by taking a few every day.
If you have a fever though, or begin to pass blood, you should go immediately to the docs as it could actually be a kidney infection rather than just a water infection especially if you also have back ache. keep an eye on it
Another pain relief tip is pee into a bowl of water, this helps the pain as it keeps the pee diluted, never tried this as couldn't work out how to without running a bath every 5 minutes, but if you have a bidet, you could try this if the pain is really bad.
hope you feel better soon.