At 4 weeks, you are not going to get your lo 100% established on EASY, they only seem to adjust more into a routine at around the 6 week age mark. Although it is good to get them started as early as possible, to teach them when is the time to E, a little A time, and to teach them to fall asleep independantly.
I would not worry too much at this age, your lo is still adjusting to the outside world.
At such a young age, it is very common for them to become drowsy and sleepy on a feed, when you see him falling asleep I would try and wind him at this stage, and this should wake him up a bit. You can then offer the feed again - this way you are ensuring that he gets a full feed. With regards to the A time - it is very minimal at this age, and is no more than a nappy change, and then you swaddle and wind down for nap time. This usually means that their whole awake time including feeding is about an hour.
With regards to getting him settled down for a nap, have you tried the Pat / Shhh technique?
Hope this info helps.
Paula