Would frequent utis (bladder infections) be caused by an std?

Almost never: Men with scarred/restricted urethra due to past STD can be susceptible to recurrent UTI, a rare complication these days. Recurrent bladder infections in women have nothing to do with past or current STD. However, in some women sex often triggers UTI, by "massaging" bacteria into the urethra. See your doctor; this is often preventable with low dose antibiotic taken after sex or 1-2 times a week.