When you are looking, one thing to think about is that males look like a doughnut and females look like a taco. Since both pop out with a bit of pressure, that alone is not enough to determine the sex.
Rabbits can be tricky to sex, especially if you don't really know what to look for. They are not too young, but younger rabbits can be harder to sex. Even experienced breeders and vets can be wrong from time to time.
If there is a breeder in your area, ask them if they can give you a hand. You can also try getting good pictures and e-mail people if you can meet (this may be hard to get good, clear photos).
If they all look the same, it could be that they are all the same sex. The next step is to determine if they are males or females.