Feeling super tired after i raced mountain bike saturday sunday. coul i be over trained?

Depending on factors: like how much you hand been training beforehand, your level of hydration, wind/temperature, how used you are to that terrain & if you pushed yourself beyond your normal training limit- it is understandable that you could feel exhausted. Additionally, unless you are accustomed to back to back racing days that can be an issue. People sometimes push themselves harder in a race than when training.