either go to a doctor and get fully diagnosed and get on medication- this is a last resort. first go to a therapist and do things that tend to make you even a little bit happy during your depressed stages and just work at making the stage transitions not so radical and then you can work on getting a little control.
1st - sorry to hear! I've been there so I personally know first hand! In order to fight depression you have to take the necessary steps. No disrespect because I've gone through it and at times I still do but depression is a state of mind not an illness! The sooner you grasp that concept the better off you'll be. Write down what you think your depressed about then on another sheet of paper write down what your grateful for! The things that gets you sad start researching on how to cope to feel better at the same time start reminding yourself how grateful you are for whatever you wrote down. Every morning i have an alarm for when I wake up to day "thank you for allowing me to live another day with my beautiful daughter" then throughout the day I say in my head and sometimes I look in the mirror and say... I love myself, I love myself, I love myself, I love myself to not allow myself through live my "short life" filled with misery" YOU have to understand, if you didn't belong on this earth you wouldn't be here, you are stronger than what you think you are, and never allow anything or anyone change that! A lot of times when one gets depressed is not an illness but simply not finding the love within yourself! You have to do some serious soul searching! It's not easy, some days are better than others, but trust me when I say you will feel so much better when your done!!! Remember - there's always sun after every storm, there's always light at the end of the tunnel! You are stronger than any state of mind and addiction!!! Good luck!!!!!