My first 3 were born within 4 years...... and at that time, (age 29), I just didn't feel that I was "done" .... so we didn't do anything permanent. (August 1982, April 1984, and August 1986.) BTW.... hubby is about 5 1/2 years older than I....
About 4 years later, we both decided it was time for another..... it was mutual, and we agreed to it.
I didn't have the difficulties of hubby being away for extended periods of time like you, and that is tough.
I will say, though.... our first 3 are girls.... and yes, we got the boy on #4.... no, we weren't trying for a boy... we would have been just as happy to have another girl. #4, the son, was born November 1991..... the day after hubby's company announced we were all (about 100 employees) being transferred from Iowa to Texas!
I love all my kids, as I know you do also, and frankly, I can't imagine my life without my son.