My personal belief is that the feeling will go away, when the feeling goes away. If you are HAVING the feeling that you want another one, then you're meant to have another one.
I truly think that there will come a time when I don't want to have another one. I'll always love me some babies, but I will be at a place where I'm done wanting to produce one of my own......I'll enjoy the babies around me. I don't know what it will be that triggers this change of feelings, but I believe I will feel it.
I'm trying to conceive #4 right now! I nursed my last baby for 18 months (which is a long time for me!) and all throughout that time I told my DH that I was done.....I felt like our third was my last. All this past spring and early summer I felt like I was done.....my husband made the apt. to get a V and I was fine with it. 2 weeks before his apt, I FREAKED out! I wanted another baby! We talked about it for a few days and he canceled his apt. and we are actively trying for #4. I am very blessed that my husband is more than happy to have a large family (he is 1 of 5) so the ball is really in my court when it comes to having more babies. And obviously you need to factor in the financial aspects of having more kids, but for me, we can always afford it because we just will! We might not have as much as we could if we weren't paying for 3 girls in dance classes and clothes for 3 kids, but we have more than enough! God will provide for my family, I truly believe that, so I don't factor the financial aspect in the decision to have another baby.
I believe that at some point I just won't feel the desire to start over with a newborn, or I won't have that feeling in my heart that my daughters are supposed to have another sibling. I will feel at peace about my husband getting a V. I'll just know.
Pray on it (if you don't pray, then meditate) and figure out if you could be at peace with not having another one. If you can't find peace, that might mean you are supposed to have another