What Causes Burning In Vagina Inspite Of Taking Treatment For UTI?

hello
i am a 29 year old female.
On march 27th, i started having symptoms of uti (burning sensation, frequent urination, slight fever). I went to my regular doctor, he gave me Cipro and took a urine sample. After I finished the treatment, I still had the burning sensation. So I called him and told him about that, he said it's probably an atypical bacteria (cause there was no bacterial growth in the urine culture) so he gave me doxicycline for another 7 days.
I'm not getting any better, the burning sensation is getting worse. The only other symptoms I have are a feeling of my urethra contracting while I urinate and sometimes I have a slight low-back pain similar to menstruation pain.
Please note that I had an episode of uti about seven months ago and it was easily resolved with Cipro.
I am otherwise a healthy person, no health issues.
Please help me, I don't know what to do.
Thank you.