Why?!?!

I really hate the way things are going. I had a miscarriage 3 years ago. My fiance and I have been trying for about a year to have a baby. Nothing so far. Not only is that discouraging but girls I work with are getting pregnant so easily. I'm talking about a 22 year old who just had a one night stand. A 18 year old who has only been with her boyfriend for 3 months. They are happy and I try to be happy for them but why not us...why can't we have kids. I'm even trying supplement and fertility drugs...there's just nothing. And everything I start my period I cry...I count down the days begging to be late. My family thinks I'm a hypochondriac because every time I experience something slightly off I question them hoping one will say it sounds like your pregnant. What am I doing wrong?