I too got a new mattress a little while ago...it was the most firm one, designed to support the back the best. wellllll....at least for now, I'm achy too when I get up. Especially between the legs, it's like someone's beat me or something! (although this definitely has nothing to do with the mattress, it's just the muscles getting all tight).
Although the feeling of waking up on a super soft squishy mattress...ow, that really makes me feel bruised all over when I wake up. It kills my hips.