At 12 weeks the uterus is just above the pubic bone so it is early to really be showing and if you are in better shape then for sure it may take longer to show :) One of my GFs showed less on her 3rd pregnancy then on her first 2 but she was working out better previous to the pregnancy... and her 3rd preg was TWINS so every pregnancy is different!!
Sex of the baby won't really factor in there. its that you are working out. So your stomach muscles are still tight.
It's probably due to you working out. Women show earlier on second children because their muscles aren't as tight. If you worked out to tighten your stomach muscles they'll have to stretch out more before you really start to pop out.
I do work out a lot more than I did before having my son. I am 5'5 125 pounds... But I just thought I would pop early since this is my second baby. Do you think it is different depending on the sex of the baby?
Every pregnancy is different. You may pop out later this time, especially if you got back in shape after your first child.
I just started my 13th week and it is just starting to really pop. I had to pull out the maternity pants because my others were so uncomfortable. Give it some time, if everything came back good I am sure you are ok. :)