UTI that wont go away even on antibiotics?

I went to the E.R about two weeks ago cause I was having all the symptoms of a painful UTI so the Dr prescribed me bactrim for 10 days. I took all my meds and after a few days I started to feel better. The pain and constant urge to pee went away well, now after 2 weeks it feels like its back or something. I also feel itchy inside (how embarrassing!) so im not sure if now I have a UTI and a yeast infection. I heard taking antibiotics will cause them. Its not as intense as it was before but i still feel that ugly pressure after urinating! and Im scared to even go pee these days. Im so so worried that it could be cancer or somethng. Im going to the Dr on Monday but its barely Saturday and Im really freaking out! why am i still having these symptoms even after taking my medication. Ive had UTIs before and bactrim has always worked for me. I forgot to mention that I also feel a weird pressure in my abdomen and I always feel like I gotta pee! Uuugh! Please someone help!!