What's Wrong With My Legs?

I've been cycling to work regularly now for over a month as well as going out most weekends for an off road jaunt, so why the hell are my legs still killing me and screaming in defiance at any incline? If getting fitter isn't one of the exciting benefits of a life of grinding physical strife day-in, day-out (over my enormous 5 mile commute...) then what's the bleedin' point? I'm already smug enough so smugging up on the carbon savings is hardly worth the bother.