The ham I had in my teens was a girl. I don't remember Spock
being in heat every 4 days either! Maybe she was a boy? But I knew boys had 'big bums'!
Fluffy is deffo a boy! I had wanted to get a girl, but he needed a new home so got him. I think i'd try getting another boy if they are generally more laid back than girls. Be better with the kids.
Yes, I did buy 3 girl gerbils once from a pet shop and one ended up being a boy, after 7 wee babies!