You have chronic urinary infections, but it may not necessarily be related to sex, except if you are having sex twice a month. It may be your anatomy, ie, the way your bladder and urethra are built up. The best thing to do is learn how to prevent the infections in a way that works for you. Washing well after sex (not just going to sleep right after), drinking tons of water, especially when you stay home and in hot days, taking showers twice a day when you get your period, loosing up your pants and underwear, etc. It's a process to learn your own body and when you do, you'll find relief. Another problem for you may be recurrent vaginitis that causes urethra burning. It may not be a UTI, but a vaginal infection that irritates your urinating routines without you noticing much change in your genitals. If I were your ob gyn, that's where I would start, teaching you how to manage chronic vaginitis.