Depression works in cycles, which I'm sure you're very familiar with. More often than not, a negative thought or experience will create more and more.
That said, the way to get out of the cycle can either be found within yourself or outside yourself:
Inside:
Meditation: start with 5-10 minutes a day to really try to be in the moment and reflect on these negative feelings. After practice meditation can act as a mental reset and a great way to get out of that cycle
Journal Writing: Another awesome way of reflection and it also acts as a collection of thoughts, so in the future you can go back and see where you were, where that stemmed from, and how you got out
Doing something new: change and novelty is always great when addressing negative cycles. Go for something you've always been curious about and try to shake-up your life
Outside:
Online Communities: /r/depression and a litany of others can be great support groups if you find the support you have IRL is not enough or those around you don't really understand depression
Therapy: I cannot express how much I value the therapy I've received in my life. Forget the stigma and feeling you're not "messed up" enough to go to someone. Whether it be Mindfulness, Behavioral, Cognitive, or Psychiatric therapy, a great therapist can really turn things around
Friends and Family: Trusting a loved one with this point in your life can both help you get out of the cycle of depression by bouncing your feelings off someone else, as well as growing your relationship with them, getting you out of the solipsism that often comes with depression
Hope this helps! Depression is a bitch, but I wish you the best