Could I have a cockerel in with my pullets?!

In April I bought six chicks. I was told they were all between 1 and 2 weeks old. I have 3 Buff Orpingtons, 2 Leghorns, and the last one I was told is an Ameraucana, but from reading here I believe she's just an EE. Since I've had them the smallest BO has been my shadow. She would jump up on top of the waterer in the brooder bin to see me when I checked on them, hop up on my knee when I'd visit the coop, etc. But just recently she has become very aggressive towards me. She stands up straighter than usual and does this little charge towards me if I try to pet her and is honestly, just plain mean. There's been no change in my routine, and someone suggested that perhaps it was a cockerel and not a pullet. Anyone have an opinion on this? (I'm going to attempt to include a pic with this post, bear with me if it doesn't come up the first time)




The one in question is the the closest BO in this pic of 4, another of the buff's in the back, hatched supposedly the same time. Any thoughts from other owners is greatly appreciated!

 

Thank you both. Hopefully she starts laying soon...I miss my baby!