At 6 weeks old, PU/PD is a little too overstimulating. You'll wanna save that method until he's 3-4 months.
At his age, I might suggest first, nix activity time. Diaper changing pretty much becomes activity time. They pretty much don't "play" in the sense you and I know it until closer to 3 months. They sort of "take in" at this point. You'll want a nice soothing naptime and bed time routine before you put him down, 10 or 15 minutes (if you can), or until he's almost asleep in your arms. In a few weeks you can try keeping him up for a little longer, I think, but not much longer. Put him down drowsy, but awake if you can, but don't fret at this point if he accidently falls asleep in your arms. Don't be afraid to use the pacifier, and don't stimulate him too much when he's awake (the bouncy chair, swing, etc. may be too stimulating for him...use it when he's a little older, you never know, he might like it then).
Think of it this way...babies, even babies a little older (mine is almost 4 months now and can only really handle being awake no more than 1.5 hours, even that's pushing it sometimes), can only stay awake 1 or 2 hours max before they become overtired. That includes feeding time. Babies that age may only be able to stay awake 45 minutes total before they start to get overtired (and 20-40 minutes of that time is feeding time). You may be able to extend the naptime if you are able to get him down not long after you feed him, if it seems that he starts getting tired right after or during the end of feeding time. Not to mention that you might be able to get him down at that "magic" moment when he just closes his eyes and falls asleep. That is always a joy to find.
It kinda sucks...you have a baby you want to enjoy, and they can't stay up long enough for you to have a lot of fun with them until they're a few months old :roll:
Hope this helps a little bit
*HUGS*
Sonya =P