I highly recommend Cognitive Behavioural Therapy. CBT is the best medicine I can afford, because all you need is pen and paper.
If you don't think you can change your circumstance, then you can try to change how you react to it. The core model of the therapy is to analyze your thoughts and look for patterns in which your brain tries to fuck with you. Identifying distortions and fallacies helps to replace your automatic thoughts with more positive ones.
Example:
Thought: I hate my job, everything about it sucks
Distortions: Overgeneralization, All-or-Nothing Thinking, Feelings as Facts
New Thought: I hate certain parts of my job, but I like X part of it
The whole thing only works if you believe in it, and the important thing is that you're not just putting a sunny face on things that make you feel terrible. You're working to restructure your thought based on objective truth.
I've struggled for a long time with the Sunday Scaries. Sometimes it feels like it's never going to get easier, and I'm going through it right now, but I know if I take the time to untangle my feelings then things end up easier in the long run.
Good luck out there, partner