Only drinks milk

Anyone else struggling to get their 2 year old to drink anything besides milk?

We've tried a LOT of different cups/sippies, different temps, water mixed with juice, just juice, different flavors, and smoothies. None of it has convinced him to take more than a sip or two.

We tried pretending to be out of milk one morning and he just refused to drink at all.

We've switched to 1% milk and added a probiotic, but it's not enough. Not getting water plus him refusing to eat fruit/veggies has caused painful pooping for him.

Dr. wants us to give him Miralax but so far he won't even finish the daily dose I'm supposed to give and I don't feel comfortable giving it to him for long anyway. Any advice out there??