the reason your photographs were poorly-lit is because
your subject was further from your camera than you had estimated.
as light travels it loses intensity, so you need to either decrease your shutter speed
( drag your shutter at a slower speed from the sync speed )
or open your lens up an additional stop to let more light in to the film.
the guide numbers on your lens probably said "x-distance use f5.6" but you were
further than whatever distance was stated for that fstop.
the next time, expose your at f2 instead of f5.6.