I don't think you're lacking in sharpness: at full size, the image you post shows sharp eyelashes and teeth. If you are using a large aperture (<F2), that explains the unsharp ears.

When you reduce the size at which the image is displayed, apparent sharpness tends to decrease. To get the impression of sharpness back, you'd have to apply some sharpening after downsizing.

Another factor is the contrast of the face, which in this case is rather low. That also tends to give the impression the image isn't sharp. Local contrast enhancement can be useful in such cases.

I wrote "impression of sharpness", as the usual sharpening techniques increase the contrast at edges in the image, which increases the acuity. It does not increase the resolution of details in your image.

There are some methods that can increase the level of detail in your image (up to a point), by using Fourier or wavelet transforms. Those methods are rather complex, slow, and can easily give rise to (very ugly) artifacts, but when applied with caution they can give you extra detail.

In summary: you could use a smaller aperture to get better depth of field, and do some editing (mainly sharpening, perhaps Local Contrast Enhancement) to counteract the effects of the low contrast and size reduction. (Even your full image as shown here isn't 26 megapixels).