post sex uti

everytime after having sex i’ve caught a uti, despite doing everything i should be doing to avoid a uti (peeing before & after sex, using protection) i still manage to get one somehow idfk how :/ i had sex day before yesterday & was so happy, i was normal the whole day yesterday but ended up with a uti today. i’ve peed in little amounts for 20+ times now within an hour, and i’m not even exaggerating.

am i doing something wrong? is there something i’m missing out on? why the hell do i keep getting a uti? is this common? please help