bad injector?
 

One of my injectors is making a clicking noise. Does that mean that the injector is bad?

not necessarally.
injectors click, its perfectly normal. just leave it be until something happens, although its unlikely

Ive also noticed ive been getting really ****** gas milage

are you sure it's your injector? usually a clicking noise is an exhaust leak...if said exhaust leak is before the o2 sensors you are sucking a crapload of air into the exhaust system whenever you're decelerating, making the o2 sensors think there's 2 much air going through the motor, and shooting a ****load more fuel into the motor