Hi E., I am sorry your baby has been uncomfortable. There is alot of misinformation about breastfeeding and diet issues, For example, eating vegetables like broccoli, which can be gas producing for us, does not cause babies to have gas because what we eat is broken down in our digestive system and nutrients are take from our bloodstream to make milk. In addition, breastfeed babies do not get lactose intolerant. It is true that they can react to dairy products, but this is to the protein in the dairy product not the lactose. Until about he age of 6 months, infants have an immature gut that allows foreign proteins to pass through,which can set up an allergic reaction. that is why waiting to introduce siolids until this time is recommended. dairy products are a common offender and it can take days for it to get out of our system. We are the only species that drinks milk past weaning age, and that is milk from a very different species. But I would not recommend an elimination diet right now unless you can determine wht the offending food is. They can be disruptive and are often not necessary.
The gassiness might not be related to your diet at all. do you pump and give expressed milk at work? Or frozen? Maybe some of this milk she has had recently is more foremilk than hindmilk, which is higher in lactose and can cause gassiness. Suggestions for positioning changes can help. Elevate her head more and see. I am sure you are a very busy mom: how long have you been back at work? make sure she finishes one breast before offering the other. If she is nursing frequently for brief periods, try offering the same breast for a couple of nursings in a row.
I would recommend trying some of the comfort measures like massage and watch for a couple days to see what happens. You can always call a la leche league leader if it continues to discuss the issue further.
Congratulations on nursing your baby and good luck!
J.