Thanks for the compliment Yishaq and at this point I would NOT suggest buying another lens so you can sleep easy.

A couple of things come to mind right away..

1 - Are you sharpening your images in a graphics program? You should.

2 - Are you aware that some camera models have a setting IN CAMERA (accessed by one of the menus) that controls sharpness (at least in mine there is). Check your manual and make sure that those settings are at neutral or adding a bit of sharpness.

Obviously you must actively focus on the area of interest for it to be sharp, but even when the subject is in sharp focus in camera, you'll likely need 'some' sharpening in a graphics program. Other things that can cause soft images include too slow of a shutter speed/camera shake.

(What lens - aperture and shutter speed did you use for that monk shot)

Let me know if you think this helps OR if you think there is a problem with your current lens.

Best!
Marko