Using the smallest aperture is not optimal for sharpness, as that causes Diffraction. Go with f/8 or f/11 for best results (it depends on the lens, and some Pentax cameras have a special "MTF" setting in the P mode for that, to always prefer the best aperture.

It could be that your "phase detection" focus measuring system is maladjusted. Therefore, try to focus using Live Mode, where a different focus system (image sensor-based) is used. If that gets you sharper images, then look in the camera's menu for a setting to adjust the focus.

And check your lens. Disconnect them from the camera, see through them by opening the aperture lever at the rear, and look for dust inside. If you see a lot of fine dust particles, it might be that your lens has gotten the dreaded mold (fungus) that can damage even the most expensive lenses. This mold causes diffusion, which you might be seeing. This mold can be removed but requires disassembly of the lens, which is rather expensive and probably not worth for a kit lens. In this case, look on the used market for a replacement. Those kit lens are cheap to come by.