can I give some guidance about the milk stuff i've been seeing but have only been skimming. I was away for 2 nights and catching up quickly.
Lactose intolerance - Lactose is milk sugar. All milks have lactose. The lactose in human milk is no different from the lactose in the milk of any other mammals. So if your baby is fine on your breastmilk but spews up formula or cow's milk, then it isn't lactose intolerance. lactase is the stomach enzyme which digests lactose, converting it to glucose so that your body can use it. All babies who are fine on breastmilk - 99.999 of babies around the world, that is, will be have this enzyme in her GI tract.
As we grow older, after the age of about 2 the amount of lactase we produce slowly reduces which is why some people become lactose intolerant.
Now, if you are still reading....
If your baby is spewing formula or cow's milk, it may be in intolerance/allergy to cow's milk protein. There is more than one type of protein in cow's milk. A true allergy or intolerance to cow's milk protein for a baby who is no longer able to get mother's milk for whatever reason can be confirmed by a RAST test which is a blood test.
DD1 had the RAST test for cow's milk protein at 8 months and it came back negative - but she was not getting any cow's milk at the time and I do not drink milk and only have small amounts of cheese. At 2yrs 8 months, the test was redone and it came back as positive but only mildly so. But now she was getting some cow's milk in her diet.