There are a few options for identifying allergy foods.
The most extreme is Total Elimination Diet (TED). Dr. Sears and Doris Rapp both have suggestions on foods to include. Basically you eat a very limited diet for about 2 weeks, and then, slowly add back in foods one at a time to see which ones cause new reactions.
And Elimination Diet (ED) is where you cut out certain foods from your normal diet. This could include any or all of the "Big 8" allergens (and I usually recommend corn in addition because it's becoming a very common allergen) and/or any foods you specifically suspect. You stay away from these foods until you reach "baseline," meaning that the allergy symptoms are gone (eczema, diarrhea, etc.). Then, add each of those foods back in one at a time and watch for reactions.
Also, it can take weeks to see improvements. Especially with dairy, it may not clear your system for 6 wks, so give it time when you do an ED that includes dairy.
In both cases, you should add back in one food at a time and consume it for 4-5 days because some reactions take longer to show up (a cumulative effect).
If you're breastfeeding, you should follow the elimination diet. If your baby is bfing and on solids, he/she should also
follow the diet.
Dairy is notoriously a problem, so if you're too overwhelmed to do a TED or ED, dairy elimination is a good first step. Also, 50% of people with dairy allergies also have soy allergies, so you might want to eliminate both at the same time.
You have to be strict on these diets. You can't cheat and have a bit of cheesecake and hope to get clear results. You have to get rid of all trace amounts and hidden sources. One site that shows alternate names for foods is: http://www.wholesomebabyfood.com/allergy.htm
and this: http://www.cornallergens.com/list/co...ergen-list.php
Food journals are really important during this time. Keep track of what you eat and when. Write down any changes in sleep, skin, bowel movements, etc. There is a lag time usually between when you eat something, and when that thing effects your baby. The time it takes to get into your breastmilk varies. For me personally, it took 3-6 hours on avg.