When i turn my head to look all the way behind me my vision goes blurry, this is not new. why does this happen and can i stop it?

See Ophthalmologist: Get thorough exam and be sure to explain your symptoms while there. Might be simple like mild astigmatism, but could be vascular insufficiency that is pronounced with head movement, even though this would be very rare in your age group. See eye specialist.

Might not stop it: It's related to the function of brain.So you might not be able to stop it.