Thats your side growth starting to kick in. the lower half of the plant will start to grow out, trying all it can to catch up to the lights. Basicly it's just your plant about to hit another life cycle...which their are many.

I can't see sign's of sex yet with those photo's. thier clear enough, but I think it's still to soon. If your side growth has not kicked in till now, then I'd say roughly another 1 and half weeks left till you'd be able to notice anything. Keep in mind though at anytime, the plant could just start to go insanly mad with a growth spurt!
In either case you still have abit of time to wait.

? for ya...
When and just how much nutes. have you given them at this point? NPK ratio? name of product?