He then decided to go to the mall. Little did he know, however, was that he was now infected with a very rare disease, which was Hormonal Transformation Syndrome. This disease would cause all of his testosterone to turn into Estrogen eventually completely transforming him into a girl.
The reason Jon did not notice this right away because he was currently wear pants. Underneath those pants, his leg hair had receded into his body. Also his legs were smaller. If he wasn't wearing his baggy pants, he would look like he had girl's legs.