Why don't my muscles ache anymore after workouts?

Hi, I've been working out for a few weeks in an effort to get into shape. During the first couple of days, I did my sets with a variety of different exercises and felt the usual swelling of the muscle, then felt some aching for a few days afterwards. Now, I do my sets and feel the "burn" that is expected, as well as the swelling, but it only lasts about half an hour and then its gone. It feels as if I'd never done them in the first place. Is this normal? Keep in mind that i have been increasing the weight, some times to the point where i can barely stand, but still no trace of it is left the next day.