Hi heatherp,
There will be a break in and adjustment period for any new mattress or sleeping system as the mattress loses any of it’s “false firmness” and the cover stretches and loosens a little and the materials settle and your body gets used to a sleeping surface that is different from what it is used to (see post #3 here). This would typically be a few weeks but it can be shorter or longer depending on the specifics of the person and the mattress (higher density materials can take longer) and it can be surprising to many people how much their sleeping experience can change over the course of the break in and adjustment period.
Unfortunately it’s not possible to “diagnose” mattress comfort issues on a forum with any certainty because you are the only one that can feel what you feel on a mattress and there are too many unique unknowns, variables, and complexities involved including body type, sleeping positions, health conditions, and individual sensitivities and preferences that can affect how each person sleeps on a mattress in terms of “comfort” and PPP (Posture and alignment, Pressure relief, and your Personal preferences) or any “symptoms” they experience so a mattress that would be “perfect” for one person may be unsuitable for someone else to sleep on. Having said that … 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.
While I don’t know which firmness level you chose … if I had to guess based on your comments and lighter weight I would say that the most likely (but not the only) reason for your symptoms would probably be comfort layers that are too firm for you and you may do better with comfort layers that are slightly softer.
If your mattress is too firm then some of the comments in post #2 here may be helpful as well.
Phoenix