You're doing fine! 6 weeks is still really young. It takes time for you and your baby to learn each others cues. Some babies are easier to read than others. Some are mellower than others. My 1st DD was a lot like your DS; she'd be perfectly happy one second and instantly screaming at top volume the next; some kids are just reactive this way. At 10, she's now my easiest child. Responding as soon as you can and with sensitivity, even if you don't know what's wrong or when their likes/dislikes change randomly, really does make a difference in the long run. It's supposed to feel horrible when they're so upset; that's a good sign that your instincts are working just the way they should!
I just have a quick question for the more seasoned mamas. When did your baby finally start understanding that you would always respond to him/her? My ds is about 6 weeks and I still don't think he knows I will take care if him, he still goes from zero to screaming in half a second, but to be fair, I don't think I have a very good handle on what it is he is screaming for most of the time., I guess I just thought AP would be more intuitive and now I wonder of I'm doing something wrong? Never felt pain like when he.screamed bloody murder lsat night before his bath (which he usually loves) and clung to my neck with a death grip...I just want him to know he's safe