Lower back ache, urgency to pee but no uti. dr said urine was clear. what could be causing urgency? could it stem from back ache or stress?

OAB possible: UTI is the commonest cause of frequeny & urgency in females.Since you do not have UTI,I would suspect what we call detrusor(the muscle wall of bladder)instablity.Bladder contracts when it shouldn't.Diagsisis made by urodynamic study. Overactive bladder gives urgency & frequency.You need to see a urologist or urogynecologist.Your condition is treatable.Good luck.