Depression is a roller coaster

To me, depression is a complicated subject. And I can pretty much relate to the people out there who's dealing with depression, it didn't started out that way, for me, it started out with anxiety back when I was in college. I only had anxiety during that time, and lots of self-doubts, then after my graduation and got my first job, anxiety manifests itself into a large scale of darkness which thus depression.

According to Google search, the signs of depressions were :

• Persistent sad, anxious, or "empty" mood [ YES ]
• Loss of interest or pleasure in activities, including sex [ YES. Writing and reading for me ]
• Restlessness, irritability, or excessive crying [ YES ]
• Feelings of guilt, worthlessness, helplessness, hopelessness, pessimism [ YES ]
• Sleeping too much or too little, early-morning waking [ YES ]
• Appetite and/or weight loss or overeating and weight gain [ YES ]
• Decreased energy, fatigue, feeling "slowed down" [ YES ]
• Thoughts of death or suicide, or suicide attempts [ YES ] 
• Difficulty concentrating, remembering, or making decisions [ YES ]
• Persistent physical symptoms that do not respond to treatment, such [ ???? ]

As you can see these signs to make me question myself that I have depression. Since as long as I could remember I wasn't happy as before, but constant sadness, even the rain, the weather I love didn't seem to cheer me up unlike before. My love for writing, didn't seem so appealing and favourable to me anymore.
And when I mean't depression is a roller coaster, it feels like a joyride, one moment you're up to the tallest peak reaching to the heavens above and then you plunge down into hell, to me that's how depression is.
Suicidal thoughts? It happens, oh the idea of taking my own life so I can be in peace. But it's hard because there's already a death in my family due to suicide, thinking about my parents, my sister suffering once I'm gone from this world. I thought of all methods to kill myself, and honestly it's scary. I even thought of writing a suicide note, how long should it be, expressing my regrets to my loved ones.