Sorry I am just getting back to you.....snowstorm here and we have had power out for days! Ugh.
Anyway, as far as how I knew DD1 just had sensitive tummy and not allergies/intolerances? Well, firstly I didn't know very much about allergies at the time, lol. But several of my family members and friends who BF said that their babies seemed sensitive to dairy and things like garlic, broccoli etc. So I ended up being careful with those foods, didn't cut them completely out, but cut down a lot, saw an improvement with her gas and tummy pains....I think I cut the foods when shr was about 3 weeks old, started babywhisperer at 4 weeks and she was sleeping through the night, taking fantastic naps, and happy as pie by 5 weeks. (wish DD2 would have followed that pattern, didn't sleep through until 16 months pretty much!). At around 12 weeks my friends were telling me I should have added all foods back weeks ago, but I was so afraid to tempt fate! I ended up just going for it, and she was fine. COMPLETELY different with Gwynnie(DD2), it wasn't just fussiness and not sleeping well, it was blood in stool, loose stool, congestion, feeding issues, .....Because of having been on BW for a couple years and seeing other mom's with similar symptoms, the minute she had blood in her stool I KNEW it was not just a virus and there was something food related going on.
It's so so hard to know for sure, but hopefully the above helps you a little bit. Have you seen the ped yet?
-xoxo