To be safe I would request (demand) a CA125 test. Most insurance will pay for it.
I had a complete hyserctomy in 2003. And from the fall of 2006 until May 2009 I had lower back pain that went through my hip & down my leg. I got tired of be doped up on pain killers, so I switched primary doctors & he did a ct scan & it picked up a 7.5 cm cyst & a complete ovary. My CRS removed them & the pain went away.... until last fall... the ovary grew back again & so did the cyst. it is now 4.4 cm. I just had the highest dosage of Lupron depot (11.25) & I go back in 2 months to see if the cyst shrank & see if my ovary stopped producing hormones. if not.... surgery again... just a thought... I have lower back pain, hip & leg pain cause of the cyst. so it is possible your back pain is from the cyst.
Your symptoms of "pelvic pain" radiating to your lower back can definitely result from a urinary tract infection to which you recieved antibiotics. Assuming you took your whole round of antibiotics you still have pain / abdominal bloating warrants futher work up!!Your Dr should repeat the urine culture just to make sure you don't have any more bacteria that may have ascended upward to one of your kidneys. If that is a clear than your Dr should have a cat scan and or an MRI done of your abdomen and pelvis. Call your Dr's office and tell them you need to speak with the Dr not a secty acting as a gate keeper. The squeaky wheel gets the oil ,unfortunately. Be aggresive and stay on top of your Dr, you have to be your own advocate. Don't forget to get copies of all your tests as you are entitled to them. Post with any further results or questions as this site has some very knowlegable people on it.
Good Luck
Kevin