I have been fighting depression since puberty so I feel your pain. Your issues may just be situational, but the fact that they keep routinely coming back tells me that your constantly on the fence and at the mercy of every new situation. The good news is that you may be close enough to mentally healthy that other natural interventions may give you more robust mental health.
Some things to check out:
The Mood Cure
GAPS Do you have gut issues? IBS, gas, D/C, etc? This line of questioning leads into the Gut and Psychology Syndrome (GAPS) approach to mental health. If you're not familiar it's pretty interesting and like Paleo made too much sense (to me) to ignore. I follow this and Paleo.
Doing a carb refeed on the weekend tends to help me boost my spirits as does bi-weekly walk/sprint sessions. The body weight work I do probably helps me feel good in my body as well.
Full disclosure is that I take Wellbutrin daily and have for years now. Paleo helped me immensely in that my medication started working finally.
Best of luck and try and stay positive. You've made a good first step by asking for support from your community. We're here for you! You are NOT alone. :-)