Maybe sometimes a talk doesn't need to happen and they're kind of just going with the flow for now. Although I have to admit a talk would have been nice sometime after he was trying to knock her up for goodness sakes. LOL.
But, yes, I get the confusion but I also remind myself that Sheldon is the king of suppression. What if he just went with Amy's off the table suggestion because he thought that's what she wanted for the time being? He seemed willing to go with the flow of things, almost like he was expecting sex would happen until she spoke up on the subject.
Just like in the last taping he told her, "whatever you want, it's your birthday..." instead of acting just as anxious as she was to get back upstairs when they were in the hallway with Lenny. Then at the end if the episode, he's VERY anxious to have sex with her again and practically runs after her into the apartment.
But now, after writing all this out, I don't even know what point I was trying to make but I'll say this, when Sheldon Cooper is in the mood for sex, BOY is he in the mood for sex. LOL.