hardly any sex what's missing between me and my husband

Hi there,
I got married 1 year back and we hardly have sex just one time a month ..My husband seems to have no interest I have talked to him regarding this but I couldn't get a proper response.. sumtimes he gets hard but while penetration he loses his erection... Am really worried and keep thinking that sumthing is wrong with me ... he loves me so much and takes good care but sex isn't there..He says am busy with work and stressed but I don know what's the connectivity ...