what to mix with milk other than sugar to give good taste
I spoke with a hospital dietitian about a study that concluded with the fact that as long as you are getting your vitamin D and calcium from other sources milk is unnecessary in the adult human diet.
She agreed and noted that lactose is hard for many people to digest and added the fats and calories can be best "spent" elsewhere.
...but if you insist...
Try making a smoothie with whatever fruits and veg you can have on this diet of yours.
If you can have cooked cereals you can either use the milk in cooking or pour over it when ready to eat.
There are recipes for puddings that are thickened with cornstarch (instead of eggs) and use cocoa as well....I have never tried this but it may be right up your alley.