Sex. Do you get tired of it ?

My husband and I have been together for 8 years. With that being said, we want to get pregnant really bad. But it's hard sometimes because we don't have sex all the time. Although I really really want a baby, my sex drive is so low. I want to have sex to get pregnant but when it's time to do the deed I get so lazy and don't wanna do anything. Has anyone else experienced this.? What could I do to make my sex drive better ?