after a few cycles and few years starting to notice more of a fatigue and laziness even feeling just flat wore out for no reason...now ive seen alot about b12 but never used it b4 if i go for injectable should i use b complex or b12 ? what dosage do i go for to start out i know nothing about b12 all i know is i feel unusually down and unmotivated and tired and hoping this is why and what i need ! ??