Why has it not happened yet? Success stories anyone?

Both me and my spouse are normal when it comes to fertility issues. Nothing wrong in that area. We have been trying for 2 1/2 years and still nothing! Intercourse is not the problem lol so I don't know what is! I'm so frustrated because within that timeframe my sister in law has conceived 2 children. It's hard and I feel like giving up! Has anyone had any success stories after years of trying?