My wife had a miscarriage in June 2010, but since she is not concieving?

I married in December 2009 and my wife had a miscarriage in June 2011. After four months we again tried for baby but since then she is not conceiving. GYN told me she is normal. She is not taking any birth control or other pills, what should I do. Should I check my semen? We are in very stress?