Hi, I thought I'd just post in here to let anyone interested know what I did and how it went.
I decided to stop all dairy and soy 3 weeks before my due date so it would hopefully be out of my system before baby arrived and I started breastfeeding.
I did this mainly cause I thought it would be easier to start without them and then test to see if he reacted.
When DS2 was about 5 weeks old I started having dairy. I would have tried it a week or two earlier but we were all sick. By this point I'd got to know him pretty well and he was a very calm and happy baby with no signs of the problems DS1 had which turned out to be due to the allergies.
DS2 was a bit unsettled the first afternoon and seriously in pain the second day. He had lots of tummy pain and also started wheezing and getting a bit of an all over body rash. So I stopped with the dairy. The next day was even worse for him but after that he quickly returned to his normal calm happy self.
So I'm pretty sure that he is allergic to dairy like DS1 was, though I'm tempted to try it again just to be sure (maybe see if he'll tolerate me having any dairy at all like bread with milk in it or something like that).
I really enjoyed having a baby who wasn't suffering and being able to easily test for the allergy.