Waking up with sore backs

This is our 5th bed that we have purchased and we had always heard about Tempurpedic mattresses being the best and most comfortable. The salesman was very educated with the details of mattresses and sold us on the new iComfort offering from Serta mainly because of the reduced smell and heat factor with these types of mattresses. Testing the two brands in the showroom felt no different. So we decided to go with the iComfort. My wife was 9 months pregnant when we bought the mattress and she was hoping it was going to help with her sleep and sore back. For the first few months, sleeping on the mattress was great. I play soccer, and with previous mattresses, the day after a game or practice, I would really notice I would be quite sore with different aches and pains. The iComfort bed solved this problem and I felt great. My wife reported feeling indifferent. Several months passed and I began to notice that the bed wasn't providing as much resistance. I felt as though I was sleeping in a valley of the bed. The middle of the bed felt like a hill and felt more resistant. By this time, my wife had given birth but she still couldn't tell whether the bed was doing anything better for her. It was getting more difficult to get out of the bed because of being sunk in more. I felt that the aches and pains that disappeared when we first started sleeping on the bed, had returned. We are now at a year with this bed. With previous mattresses, we never used to wake up with sore backs, however, sleeping on this iComfort bed over time, we now are waking up with sore backs on a DAILY basis!! My wife has complained saying that she gets up sore and notices the sinking feeling on her side as well. We have contacted the store and they were supposed to inform a 3rd party to contact me and come out to test the mattress....I haven't received a call yet and it's been a week. I'll need to follow up with them. I'm not sure what Serta can do, but we are definitely unhappy with what this mattress has done to our bodies. It is supposed to provide resistance and support while we sleep. Judging by how we feel in the morning, the iComfort isn't doing its job! Don't get me wrong, it feels like its comfortable initially and I can get to sleep, but the fact that we're now waking up with sore backs that we never had with previous mattresses is unacceptable. Beware! - Initially its good, but over time it becomes less resistant and like other reviews, it feels like you're sleeping in a sink hole.