Is it my turn yet?

My sister-in-law had her baby last night. And while I am over the moon for her and soooo excited to be an aunt; I can't help but to feel a little jealous and let down. I know it probably makes me an awful person, but I just kept thinking, when will my time come? We've been trying for 9 months, and still nothing. It's hard to stay positive when it seems like everyone around me is getting pregnant but me. Some words of encouragement would be greatly appreciated right now....