You just described me to a T!!!
We have two, and one is almost a year. I obsess constantly about another. I think mainly because I know it is a real liklihood that we may not have another. This probably makes the obsession grow even more!
I do think part of it has to do with hormones. Our make-up is such that we are programmed to reproduce. Realize your feelings are TOTALLY normal. Just because you feel this way doesn't mean you should or shouldn't have another. Sometimes women need to take the emotion out of the picture to be able to answer a question or solve a problem.
I still haven't decided. And you know, that is OK! I know this is really cheesy, but if it is meant to be, it will.
How are you all financially? And I don't mean this as a personal question or a request for you to divulge a ton of personal info - I just am asking generally, are you doing better than OK? Or, are you living paycheck to paycheck? If the latter, start saving NOW, and paying off debt. That will give you something to look forward to, and a goal! It will be fun. Then, try for another in 6 months or so. If it happens, great, the stress of money is not there!! If it doesn't, great too, you have extra money in the bank to make your family's life even easier.
My in laws don't help, neither do my parents. It is a HUGE burden raising this kids without any family help. So I do know exactly where you are coming from there. But, I wouldn't let that convince me not to bring another wonderful baby into our family.
So, after all of my rambling, I don't think you do know "when to stop". Your biological clock is going to tick regardless of your rational thought process. Talk to your husband. He should have some opinions. Right down the pros and cons for each of you. Then - I SAY GO FOR IT!!
You won't regret having another, but you may regret not.
BEST TO YOU AND YOURS!