To those who avoiding certain foods...?

treble_clef

Hi everyone.  This is the first time for me to post on this board, but I exclusively breastfed my son 5 years ago, and now my daughter.

My daughter seems to be reacting to something I'm eating.  Sometimes she gets very minor rash on her body, and her butt becomes reddish after poop.  Her poop looks different when this happen, and she gets a little fussy from needing to go very often.  Our pediatrician said I could try avoiding dairy for a week and adding it back to see if it makes a difference.  If not, do the same with soy, etc...  She also said that my daughter's condition is very mild, so I could just keep eating whatever I want and expect her to grow out of it.  

What is your experience with this?  If you avoid certain foods, how strictly are you avoiding them?  TIA!