You've had a through test of your heart, and congratulation, sounds like you have a good one.
What do you mean by palpitations that a 7 day monitor didn't pick up? Did you not experience palps when wearing the monitor, or do you claim it just didn't record there?
If a monitor can not detect what you feel I suggest the problem is anxiety or some other none cardio cause.
By 'palpitations', I'm assuming you mean PACs and/or PVCs. If that it the case, I would recommend you 1.) Try changing your diet. and 2.) Stop worrying about them.
A diet low in salt, sugar and fat helps many people out with their PACs and PVCs. Also, make sure to drink lots of water and exercise if possible. And, as you probably know, the big things to avoid are caffeine and alcohol which cause them in some people.
Not worrying about them is easier said than done but is a must if you're going to accept them. Accepting that PACs and PVCs are a part of your life and realizing that they can occur frequently and not harm you is an important part of lessening them. Or at least lessening their impact.