I agree that you should talk to your mom. There is a difference between the blues, insecurity, and clinical depression. Depression has definate symptoms that have to be present every day for at least 2 weeks. A doctor could help figure out rather quickly if this is the case or if you instead are suffering the blues and insecurity which is common at your tender age. either way, your mom or a trusted adult would be perfect to talk to. A counselor that you could tell how you feel would be great. Therapists/counselors are like your own private cheerleader that can listen and offer suggestions to feel better.
lots of luck sweetie. Your hormones are coming into play, puberty, and a general period of time (early teens) that is known to be a bit rough. So hang in there and ask for help from the adults in your life.
Talk to your Mom... let her know how you feel and that you want to talk to a Doctor about your mood swings and depression. She will understand and be helpful.