?Sex, ?hygiene. Could be: you don't urinate after sex and go to sleep with a full bladder, use bubble-bath or take tub baths rather than shower, wipe wrong way, don't spread your thighs when urinating + thus trapping urine behind labia, withhold urge to void, wear thongs or non-cotton underwear, are constipated or are menopausal. All or any of the above could make you prone tro utis.
See your doc. Don't know you, can't advise. Can be lots of reasons. Make sure these are truly bacterial bladder infections, not just the symptoms (urgency, frequency, burning). Symptoms can be from other problems, e.g. Ovariancysts or masses, uterine fibroids or masses, rectal problems, vaginal infections, e.g. Bacterial or viral. Could also be due to diaphragm, iud, kidney issues, etc.