Hi all, DS had never been given cow's milk as a drink until yesterday when I managed to forget to put my expressed BM in the fridge after work 
and it went off, so he was offered cow's milk while at the childminders. He seemed to like it - he drank a whole cup of it (which is more than he does with the EBM on some days!), but he also had very runny poo and a sore red bum that day, and this morning. It could be coincidence of course, but he's not prone to nappy rash, and he didn't have anything else unusual to eat or drink that day. He has never had any issues with milk products such as yogurts or cheese, or with whole milk with a bowl of cereal.
I'm not particularly planning on moving him off EBM and onto cow's milk, but I guess in situations like yesterday it may be needed. Is his reaction to it something to worry about? Should I be seeing the GP? Should I be trying to introduce it more gradually, or avoiding altogether for now? Or am I worrying too much? 