I've had hot pin pricks of pain up my back today. There is no visible rash. What could cause it?

Herpes Zoster. Herpes zoster which is an inflamation of the sensory nerve root by a virus called varicella/zoster can be manifested as a burning sensation mostly is very painfull, the burning then will be followed by vesicular rash takes a linear distribution following the pathway of the peripheral nerve under the skin, I advise you to see your family doctor to start the treatment with acyclovir.