Hi seanpatrick.
Welcome to our Mattress Forum! 
While there will be a certain amount of “false firmness” with any new mattress which will gradually soften (particularly in the areas where you sleep the most) and as everything "breaks in and you adjust to a new sleeping surface (see post #2 here ), the comfort layer(s) on a mattress will be doing most of the breaking in as they absorb much of compression forces that come from sleeping on it and tend to act as a “shield” for the layers below to some degree. The support layers also tend to be higher density and more durable foams and “resist” more to any “break in” processes that may occur. The most adjustment you’d notice will come from the component that is closest to your body as it undergoes the most mechanical stress. As the cover stretches and foams go through the initial softening, once this is done further softening is occurring much slower. Most of the initial break in period of a mattress as well as most of your initial adjustment (see post #3 here) period to a new sleeping surface tends to happen in the first 30 days or so in most cases, but in some cases can take a little longer.
While it’s not possible to pinpoint mattress comfort issues on a forum with any certainty because they can be very complex and there are too many unique unknowns, variables, and complexities involved that can affect how each person sleeps on a mattress in terms of “comfort”, firmness, and PPP or any “symptoms” they experience … there is more about the most common symptoms that people may experience when they sleep on a mattress and the most likely (although not the only) reasons for them in post #2 here that may be helpful.
You may wish to consider other factors such as the foundation you are using, your pillow, and in the case of memory foam the temperature of the room as well. You could check the foundation to make sure it was even and rigid or test this by trying the mattress on the floor for a few nights to see if it made a difference This being said if after the adjustment period and after ruling out some of the other possiblilities that may contribute to your discomfort, things do not improve and the soreness does not subside you may wish to consider returning the product and starting your research with the guidelines in the mattress shopping tutorial Endy also has 2" 3 lb gel memory foam in its uppermost layer which is a lower density material than I would suggest (see the durability guidelines here)
Phoenix