How i can be sure if i am depressed,i have some symptoms but i can't judge if is depression or just simple dissapointment.I also did some quiz/tests online,my score says i'm depressed.

My symptoms are,low self confidence,low self-esteem,feelings of failure,hopeless,useless,isolation,loneliness,not interestings in my life,no friendships,self insecurities,difficulties in taking decisions,difficulties in study,feeling weird with people around,low sociality,not talkative person,lost point of life,not searching for job etc.