FMIL is really annoying me-what do I do?

Me and my fiance don't want children, but his mother asks us when we are going to have them on an almost constant basis. We have explained to her that we are not going to change our minds, but she won't listen. She thinks that it is perfectly reasonable for me to give up my job (which I spent a lot of time, effort and money qualifying for) to stay home all day. I would be happy to lie to her and tell her that we are trying to have a baby but failing, but my FH says he isn't comfortable lying about that to his mother and getting her hopes up. What can I say to convince her that no amount of whining will change our minds?