Antibiotics are the appropriate medical treatment for such bacterial infections. Kidney infections can be particularly serious if not treated promptly. Other unpleasant possible outcomes of leaving a bladder infection untreated include interstitial cystitis.
As regards further investigations, a doctor should request a urine sample for testing. Has this not been done?
There is advice on reputable websites (eg. UK NHS, relevant charities) about how to reduce the risk of reinfection. This advice relates to sexual intercourse, general intimate hygiene and keeping hydrated. Some find cranberry drink (no added sugar, check the percentage juice) helpful. These are to be done alongside any prescribed treatment not instead of.