Don't worry too much about your performance. Just keep riding. You have a good 16k route, so just keep riding that. You'll get stronger and faster as you ride, and when you feel your current riding is really easy, you can add distance and ride more often. If you "compete against yourself," you can get discouraged. At first, you notice your improvement and then get discouraged when you peak and can't match your previous performance. So don't worry about it. When I started, I was riding about 12k four times a week. When that got really easy, I started increasing my distance and the number of days I ride. Now I ride almost every day, 25-35k. Sounds like you are off to a good start.