It could be a growth spurt, or that he's hit a developmental growth spurt (which is what it sounds like since you said he's more alert and started smiling). Have you heard of the wonder weeks? Google it, it describes periods of fussiness and wakefulness during times when babies hit developmental milestones. There is one around 8 weeks and sometimes they can coincide with physical growth spurts. My son just went through the 5th wonder week and what you described is exactly how he's been. He'll be 6 weeks old Friday. HTH!
Stacey, OR Nurse and mommy to Holly, 3/20/09 and Carter 12/28/12!