Is there something wrong with my Nikon D3100 auto-focus?

Hi, so about 3-4 weeks ago, my friend was sitting on the floor and she picked up the lens to my Nikon D3100 (separate from camera) and dropped it. It did not fall too far and just the lens filter was shattered. I took it to the camera store that I bought it from and they said it looked like everything was just fine and that I just needed to buy a new filter. Fast forward to NOW and the auto-focus can't seemed to come into focus and keeps on making the little noises and adjusting but has lot's of trouble coming into focus and usually makes it OUT of focus. I'm not sure if it was like this before but I don't think it was as bad. Do you think this is because of the lens being dropped or is the auto-focus not that great on some Nikon's?

Probably the drop did cause some damage or misaligned the lens elements.

Could you post some sample shots? Ideally a shot of an open book taken at a steep angle. If you then also tell where exactly on the page you focused, then that'll be very useful for a diagnosis of the autofocus system. Preferably at a long focal length (55mm) with the aperture wide open and from not too far away.

Like this:

On that shot i focused on the word "had", and the focus hit just nicely.

These devices are excellent at making photos but they're very sensitive and not made to take
physical abuse of any kind. I'd check with Nikon for repairs.

Might have damaged the focus mechanism. One thing you can try to unjam it is flip the switch on the side of the lens to manual, turn the focus ring on the lens and flip the switch back to auto. If that doesn't help, it may be time to fix or get a new lens. May be cheaper to get a new lens. If it's the kit lens, they can be bought for under $200 new, or look for a second hand lens.