My daughter was diagnosed with Lupus about 10 years or more ago. About 6 years ago went in for more tests and found out that was a FALSE Diagnosis. Long story short, she found out she was allergic to milk, milk products and anything with whey in it! She stopped eating those things and all her muscle pain, tiredness and such disappeared almost instantly.
She couldn't keep real milk down as an infant and we put her on soy milk. As she got older she switched to regular milk. She does slip up when it comes to Ice cream and takes a Lactose pill(s) before she eats ice cream or cheese.
I just don't drink milk at all. Soy or otherwise.