Well first may I just say, aren't you men just big bunch of woosies? Try being a female and having an 'internal', now that's doing it tough!
Now, your story, honestly, this is the most ridiculous things I have read on Lit in ages. I mean a doctor's room full of lit candles and a heated bed?? A gorgeous nymphomaniac nurse with a body to die for, who is more than willing to used it in the name of medical research? Let me tell you... I just loved it! It positively tickled my senses. I had to go over it twice, since the first time I was too busy reading to make any notes.
This is what I noted (the second time around):
"Robert please lie on the table with your butt as far forward as possible," she said. Also please use the supports for your feet, they help hold your legs apart and support them during the procedure. "Here goes nothing", I think to myself as I climb up onto the table, not knowing what is to happen next.
Your story slips between present and past tense. Here you slip between the two in the same paragraph. (said -past, think - present) Personally, I enjoyed your story sufficiently that it wasn't a problem, but it will really bug some readers.
You need to begin each person's new dialog with a new paragraph. It just makes it easier to read. There are some inverted commas missing too. A little later down in your story you missed them again, and there are a couple of spots where they don't need to be. It's not a big deal, but just something you need to be aware of.
I see you have your thoughts in inverted commas, most people would agree it's not necessary, and in fact it may be confused with the spoken word.
He finds my prostate, with much practiced swiftness, and proceeds to poke and probe the poor defenseless organ. I am on my tiptoes now trying to get away from His digital onslaught, but where can I go?
Call me a sick little bunny, but I really loved image. It made me smile. No wait... it made me laugh.
..we will discuss what to do about that a bit later." She said coyly.
I noticed you do this a bit too, you used a period instead of a comma. Again it's not a big deal I know, but it's something you probably should get out of the habit of.
my cock are starting
Sure it's just simple mistake, but it's distracting.
In my opinion, you have a nice and easy to read style, and a great imagination. Yes, there are a few bumps and knocks that need ironing out, but I still had to give this quirky little story of yours a well deserved five.
Your first story? Well done. I wish you well with your future writing.