It could be reflux or just digestive issues, which are both super common at this age. Ds was very colicy from 6 weeks until about 14 weeks, and then it was like he was a different baby and was suddenly happy all the time. We did put him on prevacid, but had clear reflux signs (arching the back while eating, hoarse cry even, which just means it was quite severe for him, and in fact he still needs it at 2 yrs old). We also had to hold him constantly until then. Dd is definitely getting fussier now at 4 weeks than she was a few weeks ago, but not at the level ds was. Usually her most fussy times are followed by gas, so I really do think it's all about the GI system at this age. Unfortunately, it just takes time for the gut to mature. For us, gas drops and all those things never helped. Ds also wouldn't tolerate the carrier. Dd does, thank God, though she will sometimes fight it until she has gas/poops, and then she will sleep in it for hours.
Hang in there...it should get easier in a month or so.