until you can get to your doctor and have some tests and results vitamins are a good and fairly inexpensive thing to try. like lynys says, D3, and take 2000-4000 a day (i take 2000 regularly). take some iron and some b vitamins too. and make sure you are eating enough protein.
also, could you be allergic to something in your house? i remember my doctor telling me the benefits of getting a weeks worth of southern sun should last a little longer.
and one more thing, not depression, but could it be a sort of bordom? would changing up your schedule or adding something fun to look forward to make you mentally feel better?