Expected more after only 3 years

I've had this mattress almost 3 years and it's been a disappointment. We thought it was perfect when we purchased but since then, while the mattress does not sag to the naked eye, we both roll to the center once in bed. Depending on which side of the bed I sleep on, I can only sleep "facing" the outer edge. When I do that, I at least feel like I'm sleeping "uphill". If I face towards the middle of the bed, I feel dizzy as I feel like I'm going down a hill. I might as well be sleeping on a hill. It's become the most uncomfortable bed, and it's only been 3 years, and my partner and I do not weigh 300 pounds between the two of us.