Like you said, getting the 2 implants at the same time certainly puts you in more of a unique league, let alone the fact that all your leads were put in thru one incision!
And the fact that you are getting these nausea episodes that didn't seem to be there at first.......this certainly would raise questions and your Dr needs to know that something just 'doesn't seem right' .
This is Wednesday and if you are persistent, I'm hoping they'll get to take a look at you before the weekend gets here, so you can get some anwers and if something is beginning to go wrong, it can be nipped in the bud.

Do you have a fever?

There is no doubt that you've been toughing this out, but I honestly feel that you need to be watched very carefully because of the fact that your procedure is unique to most!
PLEASE call today! At least for peace of mind and reassurance, since you are barely even 2 wks out from surgery, and I bet he's gonna attribute much of this to post op swelling........but you seem to be developing symptoms which weren't there the first 10 days.... he needs to know this.

And maybe, just maybe it's just a matter of you may have tried to do a bit too much too soon and put a bit of stress on those neck muscles?

Ask if there may be a chance that you could have a slight CSF leak, which wouldn't be the end of the world....but would sure explain the late onset of this discomfort you are getting?
I dunno, my friend.......just please call ok?