@YellowCanary have you had your vitamin D tested? I used to have psoriasis on my scalp which disappeared since getting my vitamin D up to around 60. It starts to get itchy and slightly inflamed again (but doesn't change colour) when I start to get low, like 20-30ng/mL. Look up Labor Stager (mein Direktlabor). There may be one near you. Otherwise cerascreen has been good but I'm suspicious of the accuracy of the tests.
For what it's worth I drank milk for the past two years daily but have found that, although I've tolerated it extremely well, I do better with just cheese, because the lactose seems to be fermented in some part of my intestine which is still prone to inflammation. So I would try to stick to the most well tolerated calcium sources if you have a sensitive intestine (which it sounds very much like you do). I initially was extremely lactose intolerant and was able to drink over a litre a day with virtually no issues, but as Danny Roddy has mentioned, UHT milk was always the easiest on my system. Vorzugsmilch, for example, would sometimes give me endotoxin-like symptoms like yogurt can for me, especially if I want feeling great.