Constipated 15 month old, help!!!

Hey mommas I need advice! We switched my daughter to cows milk when she was one (slowly changed her over from formula), and she became so badly constipated. I switched back to formula. I talked to me dr and he said cut down her milk during the day. I switched her back to milk and cut down the milk. But my daughter really loves her milk, so she still drinks a good amount a day. She eats pretty good, I make smoothies for her and she eats yogurt. She also drinks an insane amount of water. But she’s still constipated! It’s so bad she cries and it’ll wake her up from her sleep. She won’t drink prune juice (or any juice really) I add Miralax to her water in the morning but nothing is helping. Dr said she’s not lactose intolerant. So I’m just stuck. I’ve also tried lactaid milk, ice stayed away from almond and soy bc I’ve heard they don’t have as many vitamins as milk... help?