Can my asymmetrical face and uneven upper lip be due to muscle weakness? How can this be corrected? (photos)

Chewing predominantly on one side and sleeping on that side might contribute to muscle imbalances but remember, human faces and bodies are not perfectly symmetrical. Minor differences in facial features and body proportions are entirely normal and common.

Concerning your lips, a medialized external corner lip lift would correct this issue.

This surgery not only elevates the corners of the mouth, but increases the red lip visible on either end of the upper lip. It also decreases any displeasing downward slope the upper lip takes as measured from its center. In other words, it is quite powerful in its ability to change the shape of the upper lip, giving unprecedented control to the surgeon.

I hope this helps,
best of luck !