I was wondering if there was a disorder in which a woman becomes obsesive over having another baby? And I mean OBSESIVE

You can be obsessive about anything really, it is your mind controlling your thoughts and letting certain thoughts take over.

Some women will have a "phantom" pregnancy. They want to be pregnant so badly that their body will start to respond as if it really is.
Sometimes it doesn't get to that point, but a woman may focus so much on conceiving that sexual relations become simply a means to an end and it becomes very regimented. Watching the calendar, counting days, becoming extremely disappointed when a period arrives, set days for sex, etc. over an extended period can take its toll on a woman and on a couple.