Why is my body telling me to have a baby?

I have always wanted children but when I was about 18 and out of school I started REALLY wanting them. I think that it is a normal thing and it will probably come and go. My urge settled down for awhile till I got married then it came and went some more. Right now I've been married for 3 years and really really want children now but I know that I just have to be patient because things always happen when they are supposed to. I found that if I babysat sometimes it make it better. (especially if they were really bratty kids) I suggest starting a new hobby to distract yourself a little bit.