What would cause pvcs only when laying on my stomach? or if i bend over to grab something? it seems certain positions make them worse.

Palpitations: Palpitations have many causes from anxiety through anatomic and physiologic abnormalities. The feeling of bounding usually relates to the volume of blood pumped with each palpitation. There is no simple single answer for the question. If you're bothered by the feeling should consult a dr. To see if the problem can be clarified. It sounds like you've had a good workup and don't need to worry.

Pvcs: Pvcs in general are fairly benign unless they are effecting heart function. They are extra firing from the bottom of your heart. It would be interesting to monitor you to see if the beats you are feeling are actually Pvcs provoked on different positions and to see what they look like because some times they can be easily suppressed