I just don't know what to do anymore?

I lack the motivation to do what needs to be done. My grades are starting to suffer. I'm pretty sure I once had problems with depression before about 2 years ago. I didn't really fit in with the kids at my last school and I just felt so completely and utterly unhappy all the time. Then when we moved for my dad's job I went to a new school and I felt very accepted. But lately, those feelings of hopelessness and the lack of motivation have come back. I used to just blow it off as just being "that time of the month" but it's become a very regular thing. I have trouble focusing, I'm very irritated and started arguing with my parents about really stupid stuff. I'm getting angry at my friends for no reason. I feel to tired yet so restless at the same time. I'm scared and I don't know what to do. I don't have any thoughts of suicide so that's a plus but I'm scared my whole life is just going to fall apart and I'll return to that sad little hopeless girl I used to be.