I think there must be something intrinsic that happens right around two weeks old. Emma had diarrhea something bad almost exactly two weeks after she was born (I think she was 2w 3-4 days -- weekend from hell for us!!!). She is now 5w2d and although she still has gas pains, I swear something happened right around 4 weeks where suddenly she's able to pass it more easily! So hang in there, could be rough for another week or two...
With that said, my midwife did tell me that my diet does and will affect her. I am pretty sure the extreme gas and diarrhea episodes (which seemed to happen like every other day at that point) were after days in which I consumed things like chickpeas, spinach, loads of dairy, etc. Apparently all of those exasperate the issue for tiny tummies. I'm on a pretty boring diet now, but I can say that these days I can now eat ice cream and cheese and she seems to handle it well. I have not tried chickpeas again as those really gave her severe bouts of gas!!!