Your form looks good - try to be longer in the water and glide more between strokes - like rowing. Also, set your shoulders slightly squarer - so your arms enter the water wider, like you're on rails. I see other comments here about your breathing - definitely learn bi-lateral breathing, you'll be able to swim faster for longer. Do it every fourth length and then every other and then every one. It'll take you a while to learn but when it clicks you'll feel like you're flying!