Hi,
i’m having some problems with symmetry over x axisis. it worked well but when i closed blender and opend my file the other day, my symmetry didn’t work and it was still on, i checked and tried to disabled and than enable it, didn’t work. Don’t know what to do.
Without seeing the blend i have no idea, but you can try the following :
click on File -> New
click on File -> Append , in the file browser appearing, select your blend file
n the list that will be displayed select “Object”
In the object list select the name of your sculpt, then click on the upper right on the button “Link/Append from Library”
This will append your sculpt object into your current new session, now go to Sculpt mode and enable Symmetry on the X axis and see if it works
I tried, it doesn’t work, but I can send you a blend file.
I found the problem , it’s the origin point of your object.
The origin point is used as the center of the symmetry, and in the case of your object the origin is there :
To fix, go to Object Mode, put the 3D Cursor where you want the symmetry center to be (a simple SHIFT+S -> Cursor to Center should be enough in that case) then on the toolshelf (panel on the left) click on the “Origin” button -> Origin to 3D Cursor
Then you’ll have the sculpt symmetry working good again
Oh, thank you very much, I didn’t noticed it 
For future people with this problem:
I had this same problem and my origin was fine. I solved this by exporting OBJ and importing it again.
Thanks for that tip - worked like a charm for me.