Give her another 'dose'

Becky sits naked on the bed, and I take in the view of her flushed pink body. Her hair was already starting to dry a bit, but all and all she was still sexy. Maybe even more so.

"Are you still feeling hot, Becky?"

She gave a shrug. "A bit...but not too much."

I feel her forehead again, then say, "I don't think taking it 'Orally' did the trick..." I stick my fingers inside her, causing Becky to shudder. "I was right; you're still hot down here too. And a bit dry."

"Is that bad?"

"Very. I'll have to give you the injection...but I need to prep you." I have her lean back a bit, spread her legs and pussy lips...then I start to lick it. As she had showered, her pussy was clean and smelled of the soap we used. I make my tongue go inside her and taste her woman hood.

"D-Doctor...Ha!...it feels g-good!"

I smirk, and withdraw my tongue from her folds before gripping her hips. My rod was pulsing and twitching... "Here it comes."

With one trust I'm inside her, and I cum a minute after. Becky moans in bliss, and her pussy drains me dry...for the moment. And I fondle her breasts before sucking on her left nipple.

"I love 'Playing Doctor', with you." I tell her, before I move my hips again. "I want to always play it with you..."

"I want you to examine me, forever Doctor." Becky said, breathlessly.

"And I will! I'll examine every inch of your body...that I can promise." We both cum and I pant while pulling out of my sister. She cleans herself up and we rest a bit, before pretend to take her temperature. I tell her it's gone down a few degrees, and to change into some clothes. The pills were going to wear off, so I whisper one last order. "Through you won't remember any of the sex...you will always wish me to examine you when you feel sick and when I want too. Understand?"

"Yes...doctor..."

I leave the room when she starts to come out of trance, and go into the Exam Room to read the Doctor's Journal. There were a lot of experiments he had tried to do; such as a pill to increase pleasure, another to actually make a person have the opposite genders feature for an hour, plus many others. The few that caught my eye were a pill that could make the taker grow a certain height and the other were some to give temporary animal characteristics.

After reading a few more pages, plan started to form...