Severe Urge to Urinate?

ldy46

I am an 18 year old female and am having very severe constant urinary urgency. I had two UTIs in the last 6 months - one in October and another in December. I took antibiotics for both and they went away. Then on February 8 2017, I started feeling the constant need to pee. I thought it was another UTI coming on and went to the clinic but my urine did not show infection. I returned the next day because I had developed severe lower back pain that had gotten so bad, I could barely sit up to eat at the table or walk. I gave another urine sample, still no infection and the doctors didn't know what to think of my pain. Over the next couple weeks, my back pain went away and the need to pee sort of faded and I had about two weeks of feeling somewhat normal again. The need to constantly pee was still there but it was very slight. I was able to go to the gym and stand for multiple hours without feeling uncomfortable. Since then I have had an ultrasound done as well as my urine and blood tested and the doctor has not identified any problems with it. Then, on March 22, the urgency came back full force and has not gone away since. I do not have the back pain that accompanied it the first time but on the day it returned, I started having symptoms of what seems to be BV (bacterial vaginosis) and still have them now. I've done hours and hours of researching what this might be and I have no idea but its very very uncomfortable and upsetting. As it is now, I cannot stand for very long because the urge is so intense.
Also, I've noticed since I first started having the urgency, I never feel like my urine stream is as strong or full as it used to be and I feel like there is always more urine to come out when the stream ends. I had not had sex for over a month before this started so I'm sure it's not any sort of STD. I tried taking a considerable amount of advil to see if the urgency was being caused by inflammation but the advil had no effect on my urgency.

I would really appreciate any help anyone can offer me because my doctor has been very dismissive when I bring it up. I will have had this ailment for 2 months soon and I am really hoping to figure out what it is because I am going on a trip to Chicago in a month and would like to enjoy it. The must frustrating part is I don't even know what is wrong, so I can't treat it.

Thanks in advance.

EDIT: I have started getting slight but sharp shots of pain in my lower back on the right side, the same area as I had pain when I first started getting this urgency.