I read about bipolar disorder and its symptoms.i am 25 and i have majority of those (almost 90%).how can i be sure?what should be the next step?

Proper professional : You need to be evaluated by your doctor. He can run some screening tools and refer you to a psychiatrist for a definitive diagnosis.

Seek an evaluation: Early identification and treatment can have a significantly posibity impact on the course of illness for bipolar disorder.

Bipolar?: You need referral by your PCP to a Psychiatrist or Mental Health counselor for thorough assessment.