Sorry if this sounds a bit too "new age" but you have to find your "zen center" in your stroke. I recommend you go to the pool when you can spend some time "relaxing" with your stroke. Instead of thinking about increasing your speed, think about taking relaxing deep breaths and your muscles finding the groove of slipping through the water. Don't compete. Relax.

Most of what I observe in flawed swimming technique is excess tension. As you relax, you will begin to "discover" ways to move more gracefully through the water. When you achieve relaxation, increase your muscular output and you will be amazed how much faster you become.

Namaste.

-the "Swimming Swami"