Hi Warder45,
The mattress you purchased uses high quality materials and there are no weak links in the design but the comfort layers may be too thick or soft for you with your higher weight and it may have been “on the edge” when it was new and the normal break in period may have put you over the edge of the firmness range that is suitable for you (see post #2 here). There is only 2.25" of memory foam in your mattress but all materials will “break in” over the course of the first few weeks (not just memory foam) and become a little softer when the mattress is new (see post #3 here).
There is some information in post #2 here about the more common “symptoms” that people may experience on a mattress and some of the more common reasons for them that may be helpful but assuming that you are primarily a back sleeper the first thing I would try is a thinner pillow that doesn’t push your head as far forward and that provides good support under your neck because when you purchase a softer mattress that allows you to sink in more deeply then you may also need a thinner pillow to keep your head and neck in good alignment and prevent your head from being pushed forward which can cause neck, shoulder, or upper back issues.
Phoenix