That is exactly what happened with my daughter too - when she stopped nursing and started taking milk in a sippy cup with meals. My husband is lactose intolerant so he was the one that put it together. She stopped sleeping through the night at that time, balling up with stomach cramps screaming, crazy poo, and the worst diaper rash that I have ever seen, huge craters and cracks - had to get a prescription because nothing was working! Anyway - try giving her Lactaid brand milk, or Smart Balance - lactose free and see if it helps her. If it does then you'll know - and give it a week or two. Also - what I had to do - was have my daughter drink the lactaid if she was going to eat yogurt, cheese, pizza, ice cream etc. As long as she had a sippy cup of lactaid milk first she was ok to eat that stuff. I t was hugely inconvenient because we travel alot and you can't get lactaid in convenience stores or restaurants, we don't let her have soda,and she actually craves the milk. I finally found a product for my husband that eventually revolutionized our lives! With the lactaid brand of pills - you have to take 1-3 every time you have dairy if it has been more than 30 minutes. Expensive, and highly inconvenient! I found a product called "Digestive Advantage" - the adult formula is a tiny little caplet and you take one with breakfast and you are good to go for 24 hours! They finally came out with a children's chewable, but it's hard to find. Our Walmart used to carry it, but they only have the adult one - which at 6 my daughter is now ok to take, but Publix orders the children's chewable in for me. If you go to their website - you can print a coupon for 2-3 $ off, (it varies) and they run about $7 per box - for a month's supply. In the long run, it's cheaper and more convenient than the lactaid milk, soy, almond etc..... ALSO - before I discovered this I was giving my daughter soy milk - and then I started noticing some things, and read articles about the dangers of soy so I stopped. You can google it - but it is now being attributed to early premature puberty, certain female cancer etc. I noticed that at 3 my daughter was developing really dark hair on her arms and legs and was getting really moody. I stopped the soy all together - and the hair has gone away and the moods leveled out. Good luck!