Getting toddler to drink

Ti

Hi all I’m new to this group and a first time Mom I need advice on how to get my 18 month old to drink other fluids other than breast milk it is so difficult to get him to drink anything if it’s not my breast milk and he just doesn’t take well to cups never drank out of a bottle so he drinks out of new cups for a short time before he wants to make a mess with the juice and get it to spill out somehow I’m really out of ideas to get him to drink he has been extremely constipated because of this fact and I’m getting so frustrated on what to do to help any tips would be greatly appreciated