We dealt with this for the first couple of months with my DD. For us it also turned out to be dietary. Before I eliminated the offending foods, we used gripewater to relieve her pain (but it contains fennel, so I realize you cannot use that) but I *knew* this wasn't right or normal, so I committed to figuring out the cause.
I eliminated ALL dairy with some improvement, but still some problems. I read that many babies with dairy intolerance also react to soy, so I eliminated that too. My baby showed IMMEDIATE improvement with this!!! The first day I was off both dairy AND soy was the first time in weeks we didn't need the gripewater. It doesn't always happen this fast, but it can. And it is SO worth it to have a calm happy baby! She also slept a longer stretch that night than she ever had before. I also started keeping a food diary at the same time - tracking everything I ate and when she nursed and if she got fussy. I was able to use this to figure out some other foods she reacted to - just not as severely as the dairy and soy.
For us it was/still is onions, green peppers, tomatoes, cabbage, chocolate (even dairy free chocolate), red wine (I just had a little!) and the dairy and soy. There may be some others that I haven't quite pinned down because I have them in small quantites or rarely so the reaction is minimal.
It's true you have to really read EVERY label too! This stuff is hidden in the strangest places! Every once in a while DD will get fussy and I can't figure out why, so I'll go back and check labels on everything I've eaten and sure enough, I've missed some whey protein or casein or soy protein somewhere. She's super sensitive!
Good luck with this. I really think it is worth it to give the diet a try. It may not be this but it is easy enough to try it. Sure it is hard sometimes to go without, but there are plenty of us mamas dealing with this willing to share ideas for coping (recipes, etc.) and let me tell you, I think having a fussy baby in pain was MUCH harder on me than living without cheese