Discouraged

Been trying to conceive for the past 4 months. I had two miscarriages. And I miscarried a child that I was 3 months along on April 1, 2015. I find it frustrating when I see others are pregnant especially the ones that shouldn't or are to young. It's hard for me to see other mothers enjoying their babies. Is it normal for me to feel this way?? I gave birth to my son in January 2005 why am I having such a hard time now to conceive??