If it is a minor case of cystitus, then you may be able to 'flush' it through. Take in as much fluid as you can, at least a couple of pints every hour through the day Plain water is best, but if you get fed up with this, then flavour it very lightly with squash flavour of your choice.
Research has not found any basis for so many people's belief in Cranberry Juice. And, anything containing a lot of sugar is not good for this condition.
When passing water, try to sit upright (do not lean forward), and try to ensure you are fully emptying your bladder.
If it persists or get worse, then anti-biotics may be needed. Usually, doctors will need a sample, simply because some of these infections can be resistant to certain anti-biotics, and without a sample test there is no way of knowing this.
When showering each morning, try to turn the shower head onto that area of your body, and given it a good flush with plain warm water. If bathing, do not use any sort of bath creams or oils, etc.
Do up the amount of fluids you are taking in each day. Best way of preventing future infection is to ensure that you drink lots and lots of water every day.