I do not think there is anything wrong with breathing every stroke. I noticed that Phelps breathed every stroke when he was swimming multiple events in the same day during the Olympics. It will help you keep your heart rate down and regulate your breathing. The more you swim the easier it will get. I found that mixing in some intervals into swimming workouts helps me increase endurance and speed.

Try a couple of warm up laps then swim 25 meters as fast as you can, followed by 25 meters of recovery. Repeat 6-8 times. Then do some cool down laps. After doing this for a couple of weeks, you can time your 500 meter swim to check your progress.

You can then work up to sprinting 50 meters or 100 meters followed by a 25 meter recovery. The progress will come quickly.

Good luck!!