BMW Repair: bmw 528i, engine radiator, bmw 528i

Question
So i recently had my radiator and thermostat replaced on my 528i. It
started overheating out of no where. Now after it was replaced it still
goes to red and i turn off the car. It has an occasional shake that comes
and goes. After the radiator and thermostat was changed we put a gallon
of antifreeze and topped the rest off with water. It is loosing antifreeze
so quickly and i keep having to put more water but there is no sign of it
leaking!! I dont know if its possibly the water pump? Please if you could
please assist me in locating the problem.

Answer
If it isn't leaking externally it maybe leaking internally.You first want to make sure you have added coolant properly.You have to bleed the system of air especially since you have done all that you have done to the engine (radiator/thermostat).If it was the waterpump you would see signs of it leaking.