My 2 1/2 year old has been on Lactaid milk now for over a year. ...

My 2 1/2 year old has been on Lactaid milk now for over a year. Just after her 1st birthday she began this mysterious vomiting all the time. She did test positive for the rotavirus right around her 1st birthday but the vomiting and loose stools continued for nearly a year afterwards. So after numerous tests including a horrible one to test how much reflux she had (which came out as minimal) her docs said she must be lactose intolerant. We put her on Lactaid but the vomiting continued. It did get better but it didn't totally go away until just after her 2nd birthday. Then more than 8 months later with no throw up she came down with what I think was the 24 hour flu because she couldn't keep anything down for a full day. Took her to the docs and they said just keep her on liquids as much as possible to keep her hydrated since she also hadn't had a wet diaper in more than 12 hours. The next day she was better and finally had a wet diaper but now she complains of a tummy ache all the time after she drinks her Lactaid. At first I thought maybe it's a comfort thing since I held her so much when she had the flu but now I'm not so sure. She has been complaining now for over two weeks. The only other thing that is new for her is we are trying to potty train. She has woken up with a dry diaper for over 6 month now so we thought she would be ready. However, she is very reluctant and holds her pee for a hours after she wakes up dry. I do notice that she also has quite a bit of gas when she is complaining of her tummy hurting and her stools are firmer than they used to be. I thought maybe it was because I would buy generic Lactaid like one person mentioned but she complains even with the good stuff and even the new Organic Lactaid. She doesn't eat much dairy products other than milk. She doesn't like yogurt and rarely eats cheese and we don't give her ice-cream. So not sure what is going on?? That's why I was searching on the net and found this site. Hope someone has some suggestions for us.