my 4.5 month old baby sleep at one side and after sleep I try to reposition on back they cry and wake up what can I do

A. If you keep making your child sleep on one side the head is going to get Flat so make your child sleep on the other side not on the same side and put a heavy pillow so your child cannot change the side because if you try to change the side by putting your child on the back it will never work actually going to disturb the sleep and that is what is happening side when you make your child sleep that time it should be decided which side you are making your child sleep