UTI wont go away ?? pleasee help!?

lately i've been getting alot of uti's. i went to the doctor and i'm now on my 3rd type of antibiotics because it never went away. the dr said if it doesnt go away after this medicine i need to visit a urologist. my boyfriend and i have sex often, but i make sure to always pee before and after. i also clean the area thoroughly, as does he. we've both been tested for any sti's also. so my question is..is sex causing the infection to not go away? what can i do to help? what does a urologist do for this problem? thankyouu!