Waking up for milk?!

My almost 3yr old has barely ever woken up at night since she was born. Now around 2am every day she wakes up and wants more milk in a sippy cup and goes straight back to sleep.... Im 30wks pregnant. I feel like shes preparing me for a newborn lol but its killing me cause after im wide awake for hours. Ive tried feeding her a lil more closer to bedtime to fill her up, ive tried letting her cry it out (which results in 30mins of her crying and knocking on her door, i gave in as i didnt see it ending), ive tried explaining nicely to her she cant have more and needs to go back to sleep and she just loses it. I dont want to upset her and frankly i dont care if she wants milk, im just confused why all of a sudden she is waking up for it every night. Its been 2 weeks now. Im exhausted. Anyone else experience this with their toddler?