I'm currently going through something very similar. I'm currently using Colief drops and have found this helps. I'm also trialing colief drops with gaviscon for terrible reflux. We stopped Gaviscon at Christmas as it caused terrible constipation but we now do 1-2 sachets a day max. My next step is to cut out dairy if this doesn't improve. It's hard to tell atm as LO has a cold! My logic for using colief first was to try and establish whether it is a CMA or lactose intolerance. If you are planning on doing an elimination diet make sure to keep a diary. That was you can plot any flare ups etc, particularly as dairy is not always obviously in a lot of foods! I was told that rashes are more of a sign of CMA which my little one doesn't have. He has all the other symptoms though! My baby is also BF but I was also offered dairy free formula on prescription. It apparently tastes awful so you have to wean them off BM onto it. It's an absolute nightmare - I've been on the phone to the doctors everyday this week ❤️
I had to cut out dairy, eggs, fish and tomatoes whilst I was breastfeeding, it was ok, there are lots of vegan options in the supermarkets nowadays, I did lose a bit of weight though x