I'm sort of new to blender, and I've been following some tuts on youtube, but I've come across a problem with the grab tool in Sculpt mode. I've got the symmetry on the x axis, but when I pull the shape down, it splits down the middle, or comes down into a very sharp point. I am trying to make a human head, so that's not a good thing for me. Here's a few pics of what I mean.
http://gyazo.com/5225211a4510ef56c75a41de4d907d95
http://gyazo.com/bcb41e0cde407595fd6bcadc499a8829
Can anyone help me with this?

You want to make a jaw as I can see.
I think that you have to do sth like this
Remove the x symetry first. Second put more edge loops in edit mode for this area.
third put the shading smooth in object mode.
If it is not a character for a game I think that a subsurface modifier wouldnt be bad actually.

be patient and good luck