Hi A.,
I have a 5 week old son and he was having some similar problems. Have you talked with your pediatrician?
It could be a gastrointestinal thing. Do you eat a lot of dairy? Sometimes babies don't respond well to that. You could try cutting out dairy for a few days to see what happens. Does he burp well? I tried Mylicon gas drops and it didn't help us too much but it could help you.
Another possibility is reflux. Does he spit up? Even if not, it still could be reflux. Our son is on Zantac and I think it has helped him. He sleeps primarily in his swing and he does much better in that than in the co-sleeper we have. We also keep him swaddled the majority of the time, not just when he fusses.
I also came to realize that our little guy was getting overtired. I would get him in a sleeping position as soon as I saw him yawn once, and often even before that. he would wake up, feed, change diaper, maybe have a little awake time if he looked up for that, burp, and then get ready to go back down. He would get easily overstimulated and I needed to prep him for sleep before he got pushed over the edge, if you know what I mean.
Hope that helps!