S.,
I think it could be any of those things :) isn't the guessing game fun?!?!?!
If i were in your shoes, I would call a lactation consultant and see if they recommend a particular 'diet' or guideline of foods for nursing. they will know best what common triggers are for gas and intolerances for babies.
Secondly. your babies digestive tract just began functioning 22 days ago, with the passing of the first stool, meconium. it can be a bit sluggish, painful and gassy to get things worked out, so try some 'little tummies' gas relief drops before or after meals, be sure to burp often (I always tried to press my breast against their stomach for gentle pressure while they were up on my shoulder - stomach is on their left side) and you could try moving the legs in a bicycle peddling pattern to help push gas out. make sure not to push the legs too far up because it can make them regurgitate. Keep baby head and shoulders elevated after meals. burp after crying jags... sucking that air in is counterproductive and just makes them more farty :(
With the arching the back, frequent hiccups and spitting up, it's quite possible he has reflux. Those were my sons signs and he was put on Zantac which seemed to start working within a few hours of his first dose. Speak with your doctor about this.
And then all those other factors aside, every single one of my babies has had the evening crying spells. If you are so inclined, you could 'wear' baby with one of those wraps... i've never done this so I can't recommend a brand from personal experience, but i've seen a lot of moms recommend the Moby wrap here on mamasource. I've always just carried baby and seen it as a chance to work out my arms :)
you could try the colic hold. lets see if i can describe it. ok... baby is tummy down on your forearm with head either in the crook of your arm (better for when they have more head control) or in your hand with crotch in elbow nook and legs wrapped around your arm... this hold always seemed to calm my babies in the evenings... and if they spit up i didn't have to wear it.
Good luck to you, these trying times will be erased from memory when your little boy says 'mommy' for the first time :)