Hi dizzynyc.
Welcome to our Mattress Forum. 
We are so happy you’ve found some useful resources here!
I am sorry to hear of your shoulder pain, and glad that you’ve reached out to Nest already for a layer exchange.
It’s not really possible for us to “diagnose” a cause for your shoulder pain because there are many variables that could be involved, especially as this pain has been problematic across mattress models. Plus, there are a number of factors to consider such as your body type, variations of your sleeping positions, your sensitivity to pressure issues, and many others but post #2 here and post #6 here and post #45 here may give you some insights about what may be happening. The odds are good though that your shoulders aren’t sinking in enough to allow your torso to make firmer contact with the mattress and relieve pressure on your shoulders. Your pillow and your mattress protector or anything else you are using on top of the mattress (such as a mattress pad or topper) and even your sheets can have an effect as well.
It’s possible a softer comfort layer will be the solution here.
You can always test to see if you have a “softer” sleeping experience by moving your mattress to the floor and sleeping on it without the box spring for a few nights.
I look forward to any questions or updates you may have!
NikkiTMU