Hi Ella, you have not mentioned what is the reason for your depression and negativity in your thoughts hence lets talk about the basics of being happy always.
Firstly you have will to completely accept your situation no matter how bad it it. Thinking again and again about what is missing or whatever has gone wrong will not fix it.
Secondly minimize your expectation with people around you. Unmet expectation are the major reason for frustration and unhappiness.
If I am unable to make myself clear you can check below attached articles.That might be of help.

http://upsohigh.com/the-negativity-chain/
http://upsohigh.com/complete-acceptance/

Good Luck 🙂