when it comes to exercise I find that it takes a while (say two weeks or so) before you begin to get a pay off and the routine becomes a habit you dont want to quit. There definately is a chemical high that comes from regular exercise and this is what keeps runners on their gureling pace.
It surely will happen for you too. Also, some days are different than others, when i used to run (back in the day) some days i would fly down the road, others seemed to be endless....don't know exactly what causes this...but the way i felt after and the effects it had on my physical well being made the discomfort worth the price.