EagleRay, we found different foods caused somewhat different reactions. I knew something was wrong in the very early days (by about 2 weeks), but kept getting told that I was wrong; that breastmilk can't carry the allergens (load of bollocks, that!), that he couldn't have allergies because he was too chubby (despite being so short, he was on about 90th percentile for weight - talk about BMI issues! Again, totally wrong).
I did baby led weaning when it was time, and I found that the food he tended to avoid ended up giving him a reaction if i 'hid' it in something.... vomiting, diarrhea and eczema are our most common ones, but some like wheat and corn we didn't have those signs. In fact, i didn't realise we were still looking for an allergen when i discovered the wheat. We travelled to Aus and didn't end up eating anything with wheat for a month because we just didn't come across anything that didn't have other allergens in it. DS2 slept through the night for the first time ever. I put it down to jetlag at the time. Roll on several months and the recurrent ear infections (literally about every 3 weeks they'd both go - just enough time to heal, get infected, burst the eardrum, repeat). I'd been trying everything, and somewhere i read a list of foods that can increase the rate of infection (no allergy link mentioned, just googling). The only things we were still eating on the list were red grapes (very infrequent anyway) and wheat. Took out both of those and voila, no ear infections, sleeping through the night. Reintroduced wheat for the celiac test (at greater quantities than before); no sleeping through the night (i should point out that it used to require me sitting up for about 2 to 4 hours with him each night; he had to be upright or he was in pain), plus he started having major tantrums for no reason, that he'd never had before, and the eardrums again. I can now see a lot of behavioural issues when he eats his allergies (possibly just being in pain? not really sure; there are links showing increased ADSD signs with food allergies).
Whilst many people with eczema babies just 'treat' the eczema (creams, etc), i've found that if i remove all the allergens from his diet, his skin is absolutely beautiful. He's started at nursery now, and whilst he doesn't consume anything there that he's allergic to, there are things around (the other kids drink milk, there is dust, etc), and his eczema is back, though fairly mild.
If you haven't been doing a food diary, i highly recommend it. sometimes it will show a link to something you really didn't expect (especially as it can take days for the signs to show up).
good luck!