What could be causing blood to appear in my urine if not an infection (sometimes visible with bladder irritation) my GP is ref me to urology??

Several causes. there are several reasons for blood in urine. Your GP has done right by referring you to urologist. Please follow his advice. At your age don't delay finding the cause .
Good referral. Your GP is doing exactly what I would do for you. Let the urologist work you up and get the proper diagnosis and treatment.
Bladder stone. is probably the cause. It can make your bladder overactive. You need an ultrasound or a ct scan of the bladder . May be cystolithotripsy later on under anesthesia.