Sorry if this is long, but we have had some experience with reflux.
Do you swaddle? 4 weeks is pretty young, and he may not be fully neurologically mature enough yet to deal with all the stimulus of having hands and whatnot. (Also - have you watched the Happiest Baby on the Block? It helped us a lot.)
That being said, my son had bad reflux, and woke between 40 and 90 minutes almost every night for the first year. So I would ask you some other questions.
Does he scream after burping? Does he arch his back or try to curl up? Is he a spitter? Does he cry just before or after spitting up? Has he started to nurse more often lately, like he's having a growth spurt? If he's having a growth spurt, his little tummy may not yet be used to the amount of food he thinks he wants, and so there's a bit of time getting the balance. And if he's trying to nurse to soothe his tummy, he may be also eating a bit much and causing some overflow. My son started to develop worse signs of reflux when he was 3-4 months old and started spitting up a lot more.
Arching *usually* indicates reflux, and curling up *usually* indicates colic. The burping or spitting and then crying could indicate reflux as well. My son would never sleep on a propped mattress (he's always been a light sleeper; some babies will), and there's some evidence that if you prop it up at too high an angle they just slide down to the bottom of the angle. We put a wedge in his crib too at one point and he did better with that.
How is your baby sleeping after 7? Is he sleeping on any kind of schedule yet or is he one of those kids that takes a little longer to figure it out? He may be trying to figure out when he's tired.
And if it is reflux, expect it to get kicked up when things change physiologically - colds, teeth, viruses, etc will all kick it up a bit and then it will settle down again. It helped us a lot when we realized that and knew to expect it.
Do you carry him in a sling or anything? I found a ring sling to be awesome for when my son needed to be held for long periods of time, and it was very calming for me, too. It didn't always free up my hands as much as people can claim, but it was easier on my arms and back than just holding him as much as he wanted.
Also - do check out Harvey Karp (Happiest Baby on the Block). It seems a bit corny kind of, but it really is an awesome system for calming babies, especially under 3 months.
If any of this doesn't make sense, feel free to ask more or to tell me I'm full of it. All kids are different. We have had our own battle with reflux that we still fight - my son turned 2 in Feb and he is still on prevacid, probably for a few more months. As far as medicine goes, simethicone (mylicon) can make reflux a little worse, and 1/4 to 1/2 tsp mylanta can help, depending on the weight of the baby - but check with your pediatrician before you give your baby anything OTC. He's still really little.
And above all else, remember - it won't last forever, and enjoy your baby! They're so precious and fun!
H.