I am in the middle of rigging a characters face, i have encountered a problem when it comes to applying blendshapes

I have 3 head shapes as in the picture below, the one on the left is tthe one i am rigging, i have painted all skin weights on him and i have a slider to open/close his mouth and it looks pretty good. However when i come to apply a blend shape for the OOh or smile shape faces whn the blend shape value increases, the rigging head moves either up and down or left and right I can't understand why this would happen. I have tried deleting history on the main face and re-rigging it but the problem still arises

I tried setting a blend shape between the other two heads, and it works fine! which is really annoying! i just can't get the blend shape to the rigged head working properly without the head moving to a different location

PLEASE help!!!! been bugging me all day!!:headbang: :headbang: :headbang: :headbang: