I really don't like to exercise. And my motivation definitely comes and goes. But every month I make a commitment to exercise a certain amount (it varies month to month), and I do my darnedest to live up to that commitment.
Most months I only just make my goal or am a mere 5-10 minutes over. But I nearly always DO make it. Commitment works for me in a way motivation never did.
My 5 C's of healthy living: Commitment to conscious control, with the understanding that choices have consequences