My husband isn't interested in sex anymore

so as the title says.. ever since the birth of our daughter 15 months ago my husband hasn't been interested in sex, after the 6 weeks he was and we would do it atleast once a week but now he would happily go without and I always have to bring it up or initiate it for anything to happen but even then he's always "too tired" thing is I KNOW he masturbates! i just feel like he's not attracted to me anymore since going through pregnancy and my body changing... anyone else been through this?