18 month old doesn’t want to drink milk

My 18 month old refuses to drink milk (he can literally go 1 whole day without milk) and he only drinks milk in my helper’s room. My baby naps in my helper’s room almost everyday and I understand that he probably thinks it routine, however it’s so strange that he can go one whole day without it milk if he is unable to drink in that room. Can anyone advise me how to change his milk drinking habits?? I’ve tried offering it in a cup/with straw/bottle all to no avail. My son eats solids really well tho but I understand that milk still has to be drunk as it is the main source of calcium. I just really want to break this bad habit of his and I don’t know how. I’ve tried letting him cry before bed for 1.5hrs but he still doesn’t want the milk. Also, it’s not the milk issue cos he drinks fine in my helper’s room. I’m so confused can anyone help #18Months #formula #helpme