J.L.
I think only you know if you should have another baby, this is not something a book or anyone else can tell you. Only the 2 of you truly know the dynamics of your relationship. I would suggest a book called "the Love Dare". You did not mention if you were religious or which religion you were involved with. But this is a Christian book that was used or referred to in the Christian movie called Fireproof. I have not seen the movie, only cause I have heard mixed reviews. But I have heard great things about the book. Currently my husband and I are doing the book together and have found it is really helpful. We can not afford counseling and are trying to work on things on our own. They biggest thing is you have to want to do the book! I got a copy of the paperback for like $10. I think that if you are not really religious it is still really helpful. There are readings everyday and "dares" you must complete. they aren't religious dares (not yet) just simple things like "do not say anything negative for the whole day" then you have journal activities. We journal for the day separately, then share our thought and feelings. For $10 it may be worth a try. Remember marriage is not easy, its like a garden.... what time and effort you put into it is what you will get out of it.
Best.