It takes time to get good at endurance sports like cycling. It is said that a rider won't reach their peak for 7 years. That's 7 years of training. So relax about it a bit and stay in for the long haul. Don't get discouraged. You'll continue to experience slow improvement. The problem with getting faster is that wind resistance increases as the square of the speed. Power necessary increases as the cube of the speed. Thus a 1 mph improvement in average speed is huge. You may already be noticing increased comfort on climbs, if not a lot of increased speed. Hybrid bikes are slow. If you want a sudden big speed jump, get a road bike. Doesn't have to be new; it just has to fit you.