u are using AV mode to shoot. the shutter speed should be good enough as it is determined by the camera. I guess is your focusing. it is done not correctly.
Another way is to do spot focusing. I'm guessing that you are doing multi-point focus in these pictures?
sometimes, multi-focus does not focus on where you want to be.
change to spot focus, aim at the subject's eyes or forehead or anywhere u wan to focus.
another thing is your ISO. got to bump up yr ISO sometimes.
It could also be your handling and breathing techniques. these makes alot of difference in the sharpness.