Am I depressed?!?!?

lately, i have felt very sad and thiings that dont normally make em sad have made me sad. Like today i asked my friends if my hair was frizy and she said that it was a big frizzball and i wanted to cry. She said it as a joke tho. Alo my math grade is dropping, my teacher is asking me why but i have no idea! My friends were joking around with me and when i found out that it was all a joke i almost cried. I have been feeling very sad. I want to cry rite now. Am I?