Sir My Period Remains Only 2 Days From Last?3 Years,

Sir my period remains only 2 days from last?3 years, this problem occurs me before 3 years ago so I recommended doctor, and he take my sonographi test, everything was ok. After 1 year again my period remains for only 2 days till now, so what's d problem sir? Anything serious is there wid me? Plz answer as soon a possible, I am worried, my present age is 23. Plz reply