Help?!

So my boyfriend went to the doctor 10 days ago and found out he had a uti. Well he took the antibiotics for the 10 days and his symptoms haven’t really gone away. He went to the doctor and they sent his pee to get tested for STDS because it came back saying he has no UTI. His symptoms he still has is burning when he pees but only sometimes. Pain in his lower back and stomach aches. The doctor was making it seem like he has one and it’s stressing me out because we have had unprotected sex. I’m only 17 and I’m not sure what to do or if I should worry. He gets the results back Thursday.