+1with female preflowers you will see a little growth that looks like a calla lily, where the branches meet the stalk, it should have two fine little hairs growing out of it.
With males you will see a little seed shaped growth thats all closed up with no hairs.
If you hit search here on the forum for sexing it shouldnt be to hard to find some pictures, i would upload some but im too lazy
your plant will start to show sex usually by about week 6-7, once your branches start to alternate you should be close.
Some strains take longer than others to show sex.