Brief info: I always wished I had been born a girl
This is the story of where that wish is granted.
It's an alternate reality wherein I retain all prior memories of being a boy, plus new memories of my life as a girl. Everyone else always knew me as a girl, and my possessions changed into girl stuff.
(It's not an exact science, there will be issues, just go with it)

Not 10 minutes ago I had been an 18 year old, horny, confused boy. Now here I was standing; a 16 year old, (still horny) girl. I looked myself over in the mirror: I was skinnier and shorter than I was used to. No taller than 5'2, or maybe 5'4 at most. Auburn hair fell down past my shoulders. My clothes, which had been fitted to my body, were now too baggy. The drowned my breasts, hiding them from view.

I reached up under my shirt and ran my hands over them with excitement, loving how it felt to be touched, even by myself. I lifted the shirt up and over my head, and dropped it to the ground. I was liking what I saw in the mirrior. Plainly put; I was hot. Sexy as hell.
 
I began roughly massaging my small and firm boobs. As I did, I felt another new sensation start lower down. With excitement, I dropped my saggy and baggy jeans to the ground; my old boxers simply falling down with them. That's when I saw my own vagina for the first time. It was beatiful; I loved it. Unfortunately, a small tuft of hair was ruining the picture. This would simply not do.

So, I skipped over to my bathroom (part of my bedroom), and grabbed my razor and a bottle of shaving cream. Sitting myself up on the sink counter, I slathered some cream on my mound and started shaving away. This alone was starting to excite me and and idea sprang into my head. I looked at the razor's handle thoughtfully, but quickly rejected the idea. I looked around the counter and spotted my hairbrush. I grabbed it, and with my pubic hair only half shaved, shaving cream still all over it, I began to try and slide the brush handle up inside me.

I didn't even get it in a whole inch before it started to hurt. I quickly pulled it out. 

Deciding that I should start with something smaller, I brought my petite fingers to my love hole. I slowly slid my middle finger inside. It still hurt, but in a good way. I started sliding it in and out real slowly. I was dripping like a leaky faucet and starting to breathe pretty heavily. I added my index finger and picked up speed a little bit; sliding in and out, the inside of my pussy warmly hugging my fingers. I started going faster and faster; my other hand playing with my boobs. While still finger fucking myself, I moved away from the counter and sqautted down on the tile floor. The shaving cream and my juices were dripping all over the place, making a real mess.

I dipped my fingers into the mixture and then continued pleasuring myself. The cream created a soft burn inside me, kindling a fire of lust. Thanking God that no one was home, I began moaning loudly, whimpering in ecstasy. I Fingered myself harder and harder. Faster and faster. I finally reached my climax and gave a sort of strangled yell, and collapsed onto the floor. I laid on the floor for some time, panting heavily. I gently caressed my burning, tingling, vagina.

After some minutes, I sat up and grabbed a towel to wipe my mess off of the floor. I then grabbed my razor, and finished shaving myself, and ran my fingers over my smooth body. I left the bathroom, and walked to my dresser and picked out my new pajamas, a blue one-piece with stars and galaxies on it. Not bothering with underwear, I slipped into it, revelling in it's soft warmness. Hearing my parents come in through the front door, talking loudly, I turned the lights off, and slipped under the covers of my bed. Exhausted, I lay my head on my pillow and closed my eyes. Before falling asleep, I unzipped my pajammas. I slid my hand down to my pussy and slipped a finger up inside me. And in this manner I fell asleep, happy with my new life, and dreaming of what was to come.