help my husband barely shows interest in having sex

My husband and I have been together for 8 years and married for almost two years. We have been trying to concieve for 6 months, he is never in the mood for sex and won't initiate anything. I don't know what to do, when I bring it up it's always some sort of excuse. Weeks can go by without anything, I love this man with everything in me but am I doing something wrong for this to be happening.