I was about 13 weeks but I truly did.I have all 3 ultra sound pics 2 boys,1 girl and it was distinct deffinition.
I've found out at 16 weeks before, but I think 12 might be a little too soon.
I've had 3 children. Each child I was pregnant with I found out the "sex" of the baby in my 3rd month. But, you'll need a very willing baby.. lol & atleast a level 3 ultra sound that was done at a hospital. But it IS possible.
3 months is 12 weeks. No you won't know. You won't actually find out until your 20 week scan or in that general time frame. Sometimes they can guess early, but it's nothing more than a guess and a very generalized one and is often wrong.