Sex drive issues

So this is totally weird. I've always kinda been this way, but lately it's gotten way worse, like the past few months. I am attracted to my fiancé, I love him, I even feel turned on by him, we have no problems, but I have no want to have sex. I've never been an extremely sexual person with anyone, but lately it's gotten really bad. I will want to have sex but the drive to do it doesn't exsist, which is very incovient because we recently decided we want to have a baby, which is something I've wanted for a while. I don't know what could cause me to feel like this, or what I can do to make my self want to do it. Has anyone gone through this or have any suggestions? Like I said I'm attracted to my partner and I'm only 21.