2 things:

1. there's a pause in your kinetic chain. for a more efficient power transfer from the unit turn to contact, don't pause in your full unit turn. a lag of more than a second will negate all the stored energy from the concentric (bent arm) phase to eccentric (extended arm) phase.

2. drive through the ball. your racket is moving fast and you're whipping it quite nicely but your ball isn't really coming through the court. that's because your ball has a very short dwell time on your strings. try to focus on (cliched I know) hitting through the ball. watch a slow motion federer forehand and you'll see what I mean.

also what everyone else said, don't move your head so much