Single point auto focus point misbehaves?

. I have Nikon D3100 and usually shoot in single point autofous mode in which case the auto focus usually chooses the central dot shown in viewfinder. But time and again it erratically chooses a point either on left or right side. Then I have to reset the shooting options and it becomes ok.
Is something wrong with my camera body? How to correct it?

As far as the came ra model I use Nikon D3100, I have not found any option in the menu which enable me to tell my camera to chose any particular focus point ( which is available in Nikon D5100). But whenever I chose focus mode in AF-S and Single Point AF in AF Area mode, the came by default choses the central point. And that is where my problem lies as raised in my question.

Have you told the camera that you want to use the centre point only?

If you press the multi selector, left or right, the camera will move the focus point. See page 60 of your manual. Where is your thumb when you take pix?

Just press the center button on the multi-selector. It moves the focus point back to the center.

Read the manual and disable automatic selection of focus points. There should be a focusing mode where only the central focus point is active. Most old-timers like me can only operate a camera if that option is enabled.