See dark circles at 20 is not a big issue because basically girls at this age are often at study level that's why dark circles are normal in them and if you get plenty of sleep and still have dark circles under your eyes, that's not unusual. Fatigue isn't the only reason for under-eye circles. What appear to be under-eye circles are sometimes just shadows cast by puffy eyelids or hollows under your eyes that develop as a normal part of aging...
So i suggest you to use some eye creams like Skinmedica tns recovery complex that is a good cream and contains all natural ingredients that doesn't harm you at all...The reviews of users about this cream is positive and users found it effective...
http://www.thebeautyinsiders.com/skinmedica-tns-recovery-complex.html