I just bought a Sealy Postrepedic Mattress and I was wondering if it was normal to have backaches?

I bought a Sealy Posturepedic Ultraplush mattress from a wharehouse a few weeks ago. It’s a really nice and extremely soft mattress but my back hurts whenever I wake up. My pillows are slightly firmer and so sometimes I sleep without the pillows and that helps a little bit. I can’t take the mattress back because it was nonrefundable or nonexchangeable and plus i got a really good deal, like 40% off. Matress still looks good but is it normal? Any suggestions?
Thanks!!!