Suddenly felt weird 2 weeks before period started, then depressed, felt better 2 days after it started, now extremely depressed out of no where? Why??

AlwaysAHiddenMessage. We all can get down days, even down weeks--for all kinds of reasons(inner,outer,both), but if that feeling persists and you can still function well(work, relationships,etc)then maybe talking to a good friend will help.But if it lasts more than, say a month-or-your functioning starts to decline, you should get to a counselor 'tout suite.' It's too early to know if it's just related to your periods.
Gather more data. Connect with you OB/GYN to rule out any medical conditions. It appears that you're good at monitoring your mood. See what other changes are happening while your mood fluctuates. How is your diet, exercise, sleep, and stress. What's going on at school, work, etc? See if you can identify any triggers to your depressed mood.
Barring external. causes, this sounds like a case for an OB-GYN or internal medicine MD to check your hormones. Sounds like there might be additional psychological concerns after your period when hormones normally are less troublesome. See a psychologist after the MD.
PDS. This sounds like Premenstral Dysphoric Syndrome, although the continuation of depressed mood makes me wonder. Please see your physician about this and she can make a referral if indicated.