Antibiotics not working for UTI?

I really need some reassurance and some place to talk about this. about two weeks ago i started having urgency, a burning feeling, lower back pain... signs of a urinary tract infection, right? so i went to the doctor, they automatically gave me some macrobid. they took a sample of my urine and said that their tests showed i had a uti, but they were going to send my urine off to be tested for it additionally. the next monday my mom got a call and they said the urine sample they sent off tested negative for a uti. that is where i’m freaking out. i’m seventeen and have had two partners, without using protection. my current boyfriend only slept with one person, with a condom before me once, and my first partner was over a year ago. The macrobid did not work and so they put me on bactrum. i have two more days of this and i still feel burning and urgency. can anyone offer advice on what this is or any issues they’ve had similar? my mom doesnt know i’m sexually active and i’ve been raised in a christian household. i feel alone in this and i have been in so much pain!!