Worst Mattress Ever + Significant Back Pain

I have had (2) replacements of this mattress from the American Furniture Warehouse in a period of just a few months. I have had the same issue with each of the mattresses and am having the second one returned in order to purchase another mattress brand all together. I have had a Beautyrest in the past and it lasted a good 15 years. It was one of the best mattresses I ever had and thought that purchasing another Beautyrest would be a good idea. I was very, very wrong. I ordered a queen size Pontevedra and almost immediately, you could feel a difference between the two sides of the mattress. One side felt like it was supporting you and the other side felt like you were sinking down into it--like you were in a "valley." I contacted AFW and was given a replacement mattress of the same model. Shortly afterwards, I was noticing the same problem. The first side I laid on was fine, but when I rotated my mattress as I was supposed to, I noticed that there was extreme sagging again on the opposite side. My first purchase was less than a year ago. I have had two replacements with the same problem. I spoke with AFW and they are concerned because they said that another consumer just brought her new mattress in for the same thing. I have been waking up every morning with completely numb hands and have had a large amount of back and neck pain. Recently, I have also started to feel a deep kind of nerve pain in my back and last night I lay in my bed feeling like I was going to cry because I hurt so much. I have been tossing and turning every night since getting this model and cannot wait for my new mattress from another brand to come tomorrow--it couldn't come soon enough! I will be taking steps to contact Beautyrest asap on this, especially now that I'm learning that I haven't been alone in this and that others are experiencing the same sagging that I am with it. I'm just ready to not be in pain anymore. That is the worst part of this whole experience.