She increases the dosage and sends him on his way.

"I think you should start taking four pills a day." Dr. Valentine said as John steadied himself.
"Four? That's double what I'm taking now." John seemed skeptical.
"I know it seems like a big increase, but it's necessary for your treatment."
"If you say so."
"Great. See you the same time next week." She smiled as she ushered him out the door.

When John got home he went straight to the bathroom to have a shower. After soaping up and shampooing his hair, John's hand found there way to his stiffening cock, as was always the case when he showered. He started stroking gently until he became fully erect. He held his cock under the warm stream of water as he stroked faster and faster. It felt amazing, but something still felt off. It felt like something was missing. John brought his other hand down to his balls and started kneading and caressing. This too felt great, but something was still off. His fingers stroking against the back of his ball sack felt so good he focused all his attention there. Then he moved his fingers a little further back and found it even more pleasurable. He slowly reached further and further back. Soon he felt his middle finger make contact with his asshole and he felt a surge run all the way through his body.

He flinched for a second before his finger returned. This was it, he thought. This is what was missing. He traced his finger around his puckered rim as he stroked himself off.

"Yes. Fuck. Ugh. Yes." John panted to himself, sinking to his knees. Then John pushed hard against his puckering hole, sinking into himself.

"Oooo Daddy" He surprised himself by moaning. He had no idea where that came from, but it felt good to say. "Yes daddy. Ugh, Ooooh daddy. Harder daddy!" John moaned effeminately as he wriggled his finger deeper and deeper into himself. It didn't take long for him to cum. He shot his load directly into the shower drain as he marveled at the strength with which his tight hole squeezed around his finger. It was one of the best orgasms of his life, and he sat there for a moment with his finger still in his ass, recovering from the euphoria he had just experienced.