Let's say that you were best friends with the turtles for a while, after about a year. You had to stay with them because your were staying with April, then you tried to think of a place to move but then the turtles help you. So now you were living with them, you usually cook food for them sometimes with Mikey but sometimes they order takeout. Lastly donnie had starting making potions, sometimes the turtles sometimes drank the potions.

So one day, he had accidentally left potions, so while you were cooking you didn't had any ingredients, so you had accidentally mix the potions with the food. So all of you guys ate the food. So when you woke up, you suddenly became the opposite gender.