Don't beat yourself up.
I would like to know why many medications, both prescription and over the counter, contain lactose, even some asthma medications, when it is now a well known allergen.
My daughter is allergic to all dairy products and has to be check anything that is prescribed. The problems she had were subtle, as she reasonably healthy, but she was breathless and really struggled to climb hills. She was told she wasn't asthmatic as she didn't respond to asthmatic medication and was sent away, despite a very strong family of asthma. A nutritionist suggested avoiding dairy products and it was like magic! She had other symptoms, less obvious, which disappeared.When she introduced dairy products, very gingerly, into her sons diet, he had the same reaction she had as a baby, loose stools and very bad nappy rash all the time, so I suspect she has always had a problem. I could feel guilty, but I did the best I could with the knowledge I had at the time, as had GG.