My husband isn't that into sex...

I just don't understand.. When we first got into a relationship it was great.. We had sex a lot and it was very passionate.. Fast forword a year and it's very little.. Only at night.. In our bed in the dark and under the covers.. I know feel like he's gone off me and I'm the problem althow he swears am not.. I'm a size 20 and feel really insecure about this, I have tried to talk to him about what kinda thing he would like but he just says he's happy at the moment...