Hi there sorry you are having so much trouble
I would think that at just 3 weeks old,it really is too young to expect LO to sleep completely independantly,they really rely on knowing that you will be ther to comfort them. In a way I dont think he realises that you and him arent as one just yet,if that makes sense,its a big wide world out here and he has been used to the warmth,snugness and closeness of being in the womb.
In my opinion babies like to be swaddled (not all of course!!) as it replicates the feelings i described above..my DS is 6.5months old and im only just weaning him now..again they are all different though..
Im not an expert on what age your actions become props,but I would think they do learn very quickly.
Perhaps you are giving him too much A time and he is becoming Overtired,at that age my little one was only barely doing a feed,change and back to bed so MAYBE 45mins all up..Some of the things you describe in your post sound like overtired signs to me in a small baby,for example falls asleep very easily when on you,and wakes as soon as he gets into his bed,also staying awake for a 2 hr stroller ride, in my opinion these are classic OT signs..it's sooo easy to want to leave them up as they are so adorable at that age arent they? now,that said YOU are there with your baby every day and YOU know him much better than me
If you have a look in the FAQ section of this board there is a lot of information for newborns, I dont know how to place the link or I would but there are lots of excellent points I think you will find useful..
I hope things improve for you very soon and please let me know how it goes??