If you're suffering from depression, the book 'Feeling Good' by MD David Burns can help.
It's about cognitive-behavioral therapy, a successful treatment for depression, dealing with negative thinking patterns.
Link to PDF: http://www.mediafire.com/file/sdydy3n2mdpueck/
just find it on libgen.io
You can also try some St. John's Wort (it's a plant) tea for immediate relief (I mix mine with Melissa for the calming effect), see if it works for you.
It might also be nice to learn to meditate, as it can relieve your mind of negative thoughts. nperov.com
has some learning materials.
Or maybe you just have a vitamin D defficiency, see https://warosu.org/sci/thread/S10221251