If i'm not hungry, is that a sign that my metabolism has slowed down?

Not necessarily: If this is unusual for you, you might want to see your physician for a checkup. There are many possible reasons for appetite loss, some more serious than others. It also depends on what other symptoms might be happening concurrently, medicines/drugs you're taking, etc.

Not hungry: Metabolism changes are not necessarily indicators of appetite changes. You need thorough evaluation by your doctor to rule out endocrine, vascular and metabolic attributes can be explored.Anomalies, as well as review effects of any medications or supplements u might be taking, and if all physiological factors are ruled out, emotional.